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1 Biotechnology Unit and 2 Radiation Protection Unit, ENEA-Ente per le Nuove Tecnologie, l’Energia e l’Ambiente, Centro Ricerche, Casaccia, Rome, Italy; 3 Institute of Human Genetics, University of Goettingen, Goettingen, Germany; and 4 Institute of Pathology, GSF-National Research Center for Environment and Health, Munich, Germany
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ABSTRACT |
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INTRODUCTION |
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TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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70% of all skin malignancies. The actual risk of metastasis for these tumors is exceedingly rare, but they are locally aggressive, and 5–9% may have multiple recurrences (1)
. Although the majority of BCCs arise sporadically, several cases are attributable to the basal cell nevus syndrome (BCNS), an autosomal dominantly inherited disorder characterized by the occurrence of multiple BCCs and of extracutaneous tumors (2)
. Genetic studies on patients with BCNS have led to the identification of inactivating mutations in the human homologue of the Drosophila gene Ptch1 as the genetic defect underlying this syndrome (3
, 4)
. This tumor suppressor gene is also inactivated in sporadic BCCs (5)
. Ptch1 is a transmembrane protein that together with Smoothened forms a receptor complex for Shh. The Ptch1 protein is expressed in the cell membrane of target tissues, where it represses Smoothened signaling. Binding of Shh to Ptch1 (physiological activation) or mutational inactivation of Ptch1 (pathological activation) suspends the inhibition of Smoothened, which results in the activation of the hedgehog pathway (6) . Mutations in other genes of the pathway are also involved in the genesis of BCC. Smoothened-activating mutations have been found in 21% of sporadic BCCs and transgenic mice overexpressing mutant Smoothened develop skin abnormalities similar to BCCs (7, 8, 9) . Moreover, Oro et al. (10) showed that transgenic mice overexpressing Shh in the skin develop many features of BCNS, demonstrating that Shh overexpression is sufficient to induce BCC in mice.
Shh and its receptor complex have been shown to be expressed during many processes of embryonic development. In particular, during hair follicle morphogenesis, Shh expression correlates with hair follicle formation. A similar role for Shh signaling has been identified in the postnatal hair follicle, where its up-regulation has been recognized as a biological switch that induces resting hair follicles to enter anagen, the phase of active hair growth (11) . Although its origin is still debated, BCC has been described classically as a follicular tumor (12) .
Mice in which one copy of Ptch1 is inactivated provide an ideal in vivo model to study the typical pathologies associated with BCNS. Two independent mouse lines heterozygous for Ptch1 have recently been generated through targeted disruption of exons 6 and 7 (13) or exons 1 and 2 (14) . Analogously to BCNS patients, both mouse strains show an increased susceptibility to spontaneous tumor development (medulloblastomas and rhabdomyosarcomas) and hypersensitivity to ionizing radiation-induced tumorigenesis. In a previous study, in fact, we reported a strong enhancement of medulloblastoma development after neonatal X-ray irradiation of Ptch1neo67/+ heterozygotes (15) . Regarding cutaneous tumorigenesis, Aszterbaum et al. (16) reported a strong enhancement of BCC tumorigenesis after chronic UV exposure of Ptch1+/- (exon 1/2) mice and the appearance of microscopically detectable trichoblastoma-like tumors after exposure to a single dose of ionizing radiation. Enhancement of brain and skin tumors by ionizing radiation in mice lacking one Ptch1 copy suggests that additional genetic lesions are required for oncogenic transformation.
This study was carried out to additionally clarify the mechanisms of ionizing radiation-induced BCC tumorigenesis in Ptch1 heterozygous knockout mice generated through disruption of exons 6–7 (Ptch1neo67/+). To this aim, we used animals that were irradiated with various modalities and at different ages and followed for their entire life span. Here, we report the induction of both microscopically (nodular subtype) and macroscopically (infiltrative subtype) detectable BCCs after exposure of Ptch1neo67/+ mice to a single dose of X-rays, providing evidence of a direct causal relationship between exposure to ionizing radiation and BCC tumorigenesis. Our data demonstrate that this mouse model recapitulates the etiology and the histopathology of the human disease. Moreover, by examining the pattern of p53 protein expression and loss of heterozygosity at the Ptch1 locus in the histopathological variants of BCC, we provide new insights into the molecular bases of BCC development.
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MATERIALS AND METHODS |
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Treatment.
X-ray irradiation (HVL = 1.6 mmCu) was performed using a Gilardoni CHF 320G X-ray generator (Gilardoni S.p.A.; Mandello del Lario, Lecco, Italy) operated at 250 kVp, 15 mA, with filters of 2.0 mm of Al and 0.5 mm of Cu. Ptch1neo67/+ mice and wild-type littermates of both sexes were whole-body irradiated with 3 Gy of X-rays as newborns (4 days) or adults (90 days).
In addition, 2-month-old mice were subjected to local irradiation of the dorsal skin with a single dose of 4 Gy of X-rays. Briefly, anesthetized mice were radially positioned on a lead plate, and shaped lead shields were placed on each mouse to provide protection to the body parts to be spared. A dorsal skin area of 3 cm2 was irradiated through a central trapezoidal window of a lead shield (4-mm thickness, 60 mm in length). The shield was accurately positioned on the anesthetized mouse using its tail insertion as reference. The irradiation modalities and size of experimental groups are summarized in Table 1
. In total, the present study involved irradiation of 152 heterozygotes and 142 wild-type littermates. Groups of 52 heterozygous and 52 wild-type mice were left untreated as controls.
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Immunohistochemistry.
Immunohistochemical analysis of skin samples from infiltrative or nodular BCCs was performed on paraffin sections (4-µm thick). Before incubation in 0.3% H2O2 in methanol for 30 min, sections were dewaxed, rehydrated, and pretreated by incubation in 0.1% trypsin in 0.1% CaCl2 (pH 7.8) for 8–10 min at 37°C. Antibodies used in this study included rabbit polyclonal antibody against K14 (1:500 dilution; BabCo, Berkeley, CA), rabbit polyclonal antibody against p53 (1:500 dilution; Novocastra Laboratories, Newcastle, United Kingdom), and goat polyclonal antibody against Patched (G-19, 1:100 dilution; Santa Cruz Biotechnology, Santa Cruz, CA). Sections were incubated overnight at +4°C. Detection was carried out with the Vectastain Elite ABC Kit (Vector Laboratories, Inc., Burlingame, CA) by using rabbit or goat biotinylated secondary antibodies for 1 h at room temperature. After incubation with avidin-biotin immunoperoxidase, immunohistochemical staining was visualized with 3-amino-9-ethylcarbazole (Vector Novared kit; Vector Laboratories, Inc.), and slides were counterstained with hematoxylin.
Allelic Imbalance Analysis.
Samples from infiltrative BCCs and noncancerous tissue were frozen at -80°C. Instead, microdissection of nodular BCC-like tumors was manually performed from paraffin sections (7 µm). Briefly, dewaxed and mildly stained slides were observed with a light microscope to identify nodular BCC areas. Microdissection was conducted using a small scalpel. DNA from each sample was extracted using the NucleoSpin Tissue kit (Macherrey-Nagel, Duren, Germany) and resuspended in 40 µl of deionized water. Amplification of Ptch1 wild-type and targeted alleles was performed as described previously (15)
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RESULTS |
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. The major causes of death were medulloblastoma and thymic lymphoma (15)
. Irradiated Ptch1neo67/+ mice developed large cutaneous tumors that were classified as infiltrative BCCs, appearing as translucent scarlet papules often superficially ulcerated (Fig. 2)
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) or in association with hair follicles (FH; Fig. 3B
). Cells in the follicular/interfollicular buds were characterized by small nuclei and scant cytoplasm, the typical features of elements of the basal compartment. Hyperproliferation areas were detected in 27% of Ptch1neo67/+ heterozygous mice (Table 2)
. These microscopic lesions could only be detected by microscopic examination of the skin performed at mouse death; thus, their time of onset could not be precisely determined. However, most of them were diagnosed in mice older than 1 year (mean age: 75 weeks). These small hyperproliferations of basaloid cells were not observed in wild type mice.
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Enhancement of Microscopic Hyperproliferations of Basaloid Cells by Radiation.
None of the wild-type mice exposed to radiation developed basaloid cell hyperproliferations. In Ptch1neo67/+ heterozygotes, in contrast, exposure to X-rays resulted in a significant increase in the percentage of mice with small basaloid hyperproliferations, whose incidence raised from 27 to 53–63% (P < 0.05), depending on irradiation group. A reduction in the mean age of Ptch1neo67/+ mice with basaloid hyperproliferations was also observed after irradiation (mean age: 50 weeks). The incidence of hyperproliferation areas in the different groups is given in Table 2
.
Induction of Nodular BCCs.
Ptch1neo67/+ heterozygotes exposed to a single dose of ionizing radiation developed skin tumors with histological features of nodular human BCCs that were absent in the skin of unirradiated heterozygotes. Microscopically detectable nodular BCC-like tumors were well-circumscribed, entirely intradermic nodules of variable size and shape, showing the presence of nests of basaloid cells with peripheral palisading (Fig. 3, C and D)
. Connection with the epidermis and/or the hair follicle was often observed. The overlaying epidermis was frequently thickened and hyperplastic. The incidence of nodular lesions ranged from 21 to 47% in the different irradiation groups (Table 2)
. Tumor multiplicities determined on mice surviving 60–90 weeks after irradiation were 8.5 ± 2.9 and 2.4 ± 0.8 in the 3 Gy–90 days and 4 Gy groups, respectively. Although for both parameters there was a trend toward an increased effectiveness in mice irradiated whole body with 3 Gy X-rays at 90 days, these differences were not statistically significant. Tumor multiplicity was not calculated in the 3 Gy neonatal irradiation group because almost all mice died before 60 weeks of age.
Although we could not determine tumor latency for nodular BCCs, examination of mice irradiated as newborns, characterized by early mortality, showed that these tumors were detectable 13 weeks postirradiation. Irradiated wild-type mice did not develop nodular BCCs.
Induction of Infiltrative BCCs.
Macroscopic tumors with histological features of infiltrating human BCCs were first detected in the skin of irradiated heterozygotes 16 weeks after irradiation. As shown in Table 3
, infiltrative BCC-like tumors appeared dorsally or ventrally along the trunk. Unlike the nodular subtype, these macroscopic tumors developed only in male mice. Tumor diameters ranged from 4 to 15 mm. Incidences of infiltrative BCCs in the various groups (Table 2)
were essentially in agreement with the pattern observed for nodular tumors. BCC incidence in the 3 Gy–90 days group was 12.1%, i.e., 2.5 times higher compared with the incidence of 4.9% observed in the 4 Gy group. Although this difference was not statistically significant, a trend toward an increased effectiveness in mice irradiated whole body with 3 Gy X-rays at 90 days was confirmed for infiltrative BCCs. Irradiation of neonatal mice resulted in a low incidence of infiltrative BCCs (3.8%) because of early mortality in this group. Infiltrative BCCs showed a late onset with a mean latency of 46 weeks. The kinetics of induction of infiltrative BCCs in the different groups is reported in Fig. 4
.
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. The presence of clefts between tumor stroma and normal dermis was observed (Fig. 3E)
. Infiltrative BCC-like tumors were neither observed in irradiated wild-type mice, nor in unirradiated heterozygotes. No squamous cell carcinomas were induced by irradiation.
BCC Origin and Shh Signaling.
To confirm the basal cell origin of skin tumors, we used K14 as a basal differentiation marker. In normal skin, the basal cell layer of the epidermis, the outer root sheath, and the sebaceous glands displayed marked immunoreactivity for anti-K14 antibody (Fig. 5A)
. No immunoreactivity was detected in the remaining follicular compartments such as the inner root sheath and the bulb. Basaloid hyperproliferation areas, as well as nodular and infiltrative BCCs, showed strong immunoreactivity for anti-K14 antibody, suggesting a common progenitor for all basal cell lesions observed (Fig. 5, B–D)
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, indicating that this phase is dependent on Shh pathway expression. Strong Ptch1 expression was also observed in basal cell hyperproliferation areas and nodular BCC-like tumors during anagen (Fig. 6, A and B)
. No Ptch1 expression was detected in the epidermal basal compartment, hyperproliferation areas, and nodular BCC-like tumors during telogen, the resting phase of hair cycle (Fig. 6, C and D)
, supporting the notion of temporal control of Shh pathway expression during postnatal hair follicle growth.
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. In contrast, analysis of radiation induced nodular and infiltrative BCCs showed an intense, dispersed pattern of p53 protein expression in 88% (7 of 8) of nodular and 100% (7 of 7) of infiltrative BCCs (Fig. 7, B and C)
, suggesting a possible involvement of p53 in the formation of these tumors. The intensity of overall staining was similar in nodular and infiltrative subtypes.
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. All infiltrative BCCs developed in these experiments were examined for their allelic status at the Ptch1 locus. Fig. 8B
shows loss of the wild-type Ptch1 allele in 100% of infiltrative BCCs (9 of 9).
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DISCUSSION |
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TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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To clarify the mechanisms by which ionizing radiation induce BCC development, control and irradiated Ptch1neo67/+ mice and wild-type littermates were monitored for their whole life span. Particular attention was paid to skin abnormalities, and skin samples were analyzed at mouse death. The skin of unirradiated Ptch1neo67/+ mice was macroscopically normal, and only microscopic examination showed the presence of hyperproliferations of basaloid cells arising from both the hair follicles and the interfollicular epithelium. These occurred in 25% of mice.
The interaction of ionizing radiation with Ptch1 deficiency resulted in a strong alteration of the skin phenotype. Development of basaloid hyperproliferation areas (Fig. 3, A and B)
was enhanced by X-rays, and their incidence increased to 53–63% depending on irradiation group. No difference in morphology was observed in microscopic lesions from unirradiated or irradiated mice. In addition, the skin of irradiated Ptch1neo67/+ heterozygous mice showed the occurrence of microscopically detectable, intradermal, well-circumscribed nodular BCCs (Fig. 3, C and D)
, as well as of large infiltrative BCC-like tumors (Figs. 2
and 3, E and F
). Neither of the last two histological subtypes was found in unirradiated Ptch1neo67/+ heterozygotes, demonstrating a direct causal relationship between ionizing radiation exposure and BCC development.
Deregulation of the Shh pathway has been closely linked to BCC development, but the mechanisms of BCC tumorigenesis have not been completely clarified yet. As shown by microscopic skin alterations in unirradiated Ptch1+/- mice, deregulation of the Shh-Ptch pathway represents the initiating step in BCC development and constitutes a rate-limiting event in BCC formation. However, it is not by itself sufficient for full BCC development in Ptch1+/- mice (9)
. Our tumor data from irradiated Ptch1neo67/+ heterozygotes (Tables 2
and 3
) identify hyperproliferation areas as the most frequent type of basal cell lesion, followed by nodular and finally by infiltrative BCCs, the least frequent subtype. In addition, although multiple nodular BCCs developed in each mouse, infiltrative BCCs developed always as solitary tumors. Finally, although our experimental approach did not allow direct determination of the latency for microscopic tumors, our results suggest that nodular BCCs have shorter latency compared with infiltrative BCCs. In mice irradiated neonatally (3 Gy), nodular BCCs appeared as early as 3 months after irradiation, and 7 of 11 independent nodular tumors were detected in mice that died before 6 months of age (data not shown). Instead, infiltrative BCCs showed a delayed onset, with 7 of 9 ionizing radiation-induced tumors developing in mice older than 10 months, paralleling the human situation where BCC is mainly a disease of the elderly. These findings are consistent with the hypothesis of chronological tumor progression from tumor precursor lesions toward overt neoplasias, with epidermal hyperproliferation areas and nodular and infiltrative BCC-like tumors representing different stages of BCC development.
The expression of Shh protein in normal skin is subject to tight spatial and temporal regulation (18
, 19)
, being restricted to cells at the distal portion of the growing hair follicle and to the anagen hair growth phase (20)
. Shh induces transcription of target genes, including Ptch1 itself, by antagonizing the activity of Ptch1. Immunohistochemical analysis of Ptch1neo67/+ skin showed positive Ptch1 staining of the outer root sheath of hair follicles and of microscopic basal cell lesions (i.e., basaloid hyperproliferations and nodular BCCs) only during anagen. In contrast, no Ptch1 staining was observed during telogen-stage skin (Fig. 6)
, suggesting temporal regulation of Shh signaling in both growing hair follicles and in epidermal hyperproliferation areas and nodular BCCs. These observations are similar to those reported for Ptch1+/- mice (exon 1/2; Ref. 19
) and suggest that Shh pathway activation in the skin of Ptch1neo67/+ heterozygotes is still anagen restricted and that haploinsufficiency is not by itself sufficient to cause constitutive activation of the pathway. In contrast, marked up-regulation of Shh target genes is a hallmark of full-blown BCC. This suggests that modestly deregulated Shh signaling plays a role in the development of basaloid hyperproliferation, but a critical threshold of signaling activity must be achieved for full BCC development. Recent studies have pointed out the importance of the level of hedgehog pathway deregulation in the development of basal cell tumors and the need of high levels of Shh signaling for the sustained, expansive tumor growth characteristic of BCCs (9
, 21)
.
The appearance of nodular and infiltrative BCCs in the skin of irradiated Ptch1neo67/+ mice suggests that development of these tumors requires additional genetic lesions, consistent with the fact that tumor development is believed to require a number of genetic alterations. In human BCCs, the tumor suppressor gene p53 is frequently mutated (22
, 23)
, suggesting that p53 mutations are an early and required event in BCC tumorigenesis. In the mouse, p53 gene mutations were detected in BCCs induced by long-term UV exposure in Ptch1+/- mice (exon 1/2; Ref. 16
). Nilsson et al. (21)
, in contrast, failed to detect p53 mutations in spontaneous BCCs from K5-Gli-1-transgenic mice. In this study, immunohistochemical analysis of p53 expression showed intense p53-positive staining in nodular and infiltrative BCC-like tumors but not in hyperproliferation areas (Fig. 7)
, suggesting that altered p53 signaling may be a prerequisite also for murine BCC. Surprisingly, there was no correlation between expression level and tumor aggressiveness because the pattern of p53 staining was similar in nodular and infiltrative BCC-like tumors. This contrasts with a study of relation of p53 expression to the aggressive infiltrative histopathological feature of human BCC (24)
.
BCNS patients inherit one copy of mutated Ptch1 and develop BCC mainly after exposure to UV or ionizing radiation when the remaining wild-type copy is mutated or deleted in epidermal keratinocytes. Although limited data exist for BCC development in Ptch1 heterozygous knockout mice, loss of heterozygosity at the Ptch1 locus after UV or ionizing radiation has been implicated in BCC tumorigenesis (16)
. We analyzed ionizing radiation-induced infiltrative BCCs for the allelic status at the Ptch1 locus and detected loss of the wild-type Ptch1 allele in all infiltrative BCCs examined (9 of 9; Fig. 8B
). Our results confirm that the Ptch1 gene is an important target of radiation and that cells lacking both Ptch1 alleles undergo clonal expansion leading to uncontrolled growth and local invasion. In view of the development of different types of skin lesions in irradiated Ptch1neo67/+ heterozygotes, we next investigated the status of the wild-type Ptch1 allele in the nodular, microscopic subtype. Analysis of 10 microdissected nodular BCCs showed retention of the wild-type allele (Fig. 8A)
, indicating that other factors must contribute to this step of neoplastic progression. These results, taken together with the latencies of skin lesion development, suggest that tumor type may be dependent on quality and quantity of additional acquired mutations and that irradiated Ptch1neo67/+ epidermis is more permissive to accumulation of additional oncogenic mutations, including loss of wild-type Ptch1. This may be a consequence of increased genomic instability associated with altered p53 signaling, which may enhance the rate of acquisition of secondary mutations.
Our results strongly support the hypothesis of a process occurring through the accumulation of genetic alterations reminiscent of that seen in colorectal cancer (25) in which a crucial role has been attributed to mutations activating the Wnt pathway that shares many similarities with the Shh pathway (26) . Although the concept of BCC tumorigenesis as a multistep process conflicts with the lack of premalignant lesions reported for BCCs (27) , this hypothesis has recently been suggested for human BCC (28) .
In contrast to mouse models overexpressing nuclear mediators of Shh signaling (e.g., K5-Gli-1-transgenic mice; Ref. 21
), showing rapid and frequent appearance of BCC-like growths during late embryogenesis, the frequency of spontaneous basaloid hyperproliferations in Ptch1neo67/+ mice was relatively low and delayed. Although requirement for additional genetic damage can be postulated even at this early stage, we favor the hypothesis that deregulation of this pathway at a proximal level may be less effective than deregulation at a distal level (e.g., Gli-1, Gli-2; Refs. 21
, 29
). Consistent with this supposition is the finding that Shh target gene induction in Ptch1 heterozygotes maintains normal hair cycle dependence (Fig. 6
; Ref. 19
), which appears to be a key mechanism for accurate control of morphogenesis and renewal of hair follicle. In keeping with this view, the X-ray-induced enhancement of basaloid hyperproliferations may be due to a Shh-mediated mechanism of tissue repopulation after radiation damage analogous to that operating in the airway epithelium after injury caused by chemical damage (30)
, rather than being associated with secondary genetic hits.
A surprising outcome of our study was the strong effect of gender on radiation-induced BCC tumorigenesis. Although microscopic basal cell lesions were observed in males and females, infiltrative BCCs only developed in males. Male sex is a known risk factor for BCC also in humans (31) and is associated with more BCC/year (rate ratio: 1.2). Although the role of estrogens in the development of skin cancer is controversial (32) , our results point to an effect of hormonal status on BCC development, consistent with recent findings showing that Ptch1 is involved in the response to steroid hormones such as estrogens and progesterone and also to their precursor, i.e., cholesterol (33 , 34) . Additional experimentation is needed to consolidate the possibility of involvement of Shh-Ptch1 signaling in hormone-induced susceptibility to BCC development.
An additional important observation is the difference in BCC induction between mice irradiated locally at 60 days and mice irradiated whole body at 90 days. Although not statistically significant, higher incidence of both nodular and infiltrative BCCs were observed in the latter group, which may point to a relationship between radiation susceptibility and age-dependent hair growth cycle phase (35) . On the basis of this hypothesis, mice in a growth phase of the hair cycle (90 days) may be more susceptible to BCC induction compared with mice in a resting phase (60 days). This age dependence is likely to reflect the ability of hair progenitor cells to express the hedgehog pathway and proliferate at the time of irradiation (36) . Age-dependent susceptibility to BCC induction would imply a strong concordance with the cellular mechanisms of induction of medulloblastoma by ionizing radiation in Ptch1neo67/+ mice in which a tumorigenic window of sensitivity reflects the time-limited ability of tumor precursor cells to proliferate (15) . Alternately, immunosuppression due to whole-body irradiation might contribute to increase BCC risk (37) . To discriminate between these two hypotheses, it will be of interest to examine skin tumor development in mice irradiated locally (a) in growth phase of the hair cycle, or (b) after induction of an artificial growth phase by hair plucking, or (c) by administration of chemical inducers. Experiments are presently underway to investigate hair cycle-phase/immunosuppressive effects.
Finally, in this study we show that mouse lines obtained through deletion of exons 6/7 do not show substantial differences in BCC tumorigenesis compared with Ptch1+/- (exon 1/2) mice (16) . However, whereas a single X-ray dose was able to induce large, infiltrative BCCs in Ptch1neo67/+ mice (this study), Ptch1+/- mice only developed microscopic BCCs. The mouse age at irradiation (60 days) and the low number (n = 18) of exposed mice are likely to be responsible of the absence of macroscopic BCCs in the former study. Another potential explanation could be the genetic background on which Ptch1+/- mice (exon 1/2) were generated (16) .
In summary, we provided evidence that BCC tumorigenesis in Ptch1neo67/+ heterozygotes occurs in a multistep fashion. Our data regarding incidence, multiplicity, and latency of the different basal cell lesions, as well as the results of our analysis of p53 protein expression and Ptch1 allelic status in nodular and infiltrative BCCs are consistent with a model in which (a) Ptch1 haploinsufficiency, by causing modest deregulation of the Shh pathway, determines development of BCC precursor lesions, i.e., basaloid hyperproliferation areas in untreated mice during anagen phase, but it is not sufficient to drive full BCC development; (b) after direct genetic damage by radiation in genes serving critical functions in the regulation of cell proliferation, apoptosis, response to DNA damage such as p53, BCC precursor lesions progress to nodular, intradermic BCCs; (c) genomic instability associated with p53 mutation promotes complete loss of Ptch1 function, with constitutive activation of the Shh pathway and progression to large, invasive BCCs. This multistep model provides the opportunity to dissect out the molecular events underlying stepwise progression from precursor lesions to full BCC development. Finally, the development of a model in which BCCs develop in mice within the first year of life after a single X-ray exposure provides a useful tool for the study of both the pathogenesis and treatment of this very common human tumor.
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FOOTNOTES |
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The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Note: M. Mancuso and S. Pazzaglia contributed equally to this work.
Requests for reprints: Anna Saran, Biotechnology Unit, ENEA CR-Casaccia, Via Anguillarese 301, 00060 Rome, Italy. Phone: 39-06-30484304; Fax: 39-06-30483644; E-mail: saran{at}casaccia.enea.it
Received 8/ 7/03. Revised 10/ 6/03. Accepted 11/17/03.
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C. Adolphe, R. Hetherington, T. Ellis, and B. Wainwright Patched1 Functions as a Gatekeeper by Promoting Cell Cycle Progression Cancer Res., February 15, 2006; 66(4): 2081 - 2088. [Abstract] [Full Text] [PDF]
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P.-L. So, K. Lee, J. Hebert, P. Walker, Y. Lu, J. Hwang, L. Kopelovich, M. Athar, D. Bickers, M. Aszterbaum, et al. Topical Tazarotene Chemoprevention Reduces Basal Cell Carcinoma Number and Size in Ptch1+/- Mice Exposed to Ultraviolet or Ionizing Radiation Cancer Res., July 1, 2004; 64(13): 4385 - 4389. [Abstract] [Full Text] [PDF]
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S. Pazzaglia, M. Mancuso, M. Tanori, M. J. Atkinson, P. Merola, S. Rebessi, V. Di Majo, V. Covelli, H. Hahn, and A. Saran Modulation of Patched-Associated Susceptibility to Radiation Induced Tumorigenesis by Genetic Background Cancer Res., June 1, 2004; 64(11): 3798 - 3806. [Abstract] [Full Text] [PDF]
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; C). Higher magnification of tumor in B: cell cluster with typical peripheral palisading pattern (D). Infiltrative BCC-like tumor characterized by an aggressive growth pattern. The tumor deeply infiltrates below the dermis. Cleft between normal dermis and tumor stroma (
