Low frequency of genetic change in p53 immunopositive clones in human epidermis

Molecular pathology of skin neoplasms of the head and neck

CONTEXT

Skin neoplasms include the most common malignancies affecting humans. Many show an ultraviolet (UV)-induced pathogenesis and often affect the head and neck region.

OBJECTIVE

To review literature on cutaneous neoplasms that show a predilection for the head and neck region and that are associated with molecular alterations.

DATA SOURCES

Literature review.

CONCLUSIONS

Common nonmelanoma skin cancers, such as basal and squamous cell carcinomas, show a UV-induced pathogenesis. Basal cell carcinomas are characterized by molecular alterations of the Hedgehog pathway, affecting patched and smoothened genes. While squamous cell carcinomas show UV-induced mutations in several genes, driver mutations are only beginning to be identified. In addition, certain adnexal neoplasms also predominantly affect the head and neck region and show interesting, recently discovered molecular abnormalities, or are associated with hereditary conditions whose molecular genetic pathogenesis is well understood. Furthermore, recent advances have led to an increased understanding of the molecular pathogenesis of melanoma. Certain melanoma subtypes, such as lentigo maligna melanoma and desmoplastic melanoma, which are more often seen on the chronically sun-damaged skin of the head and neck, show differences in their molecular signature when compared to the other more common subtypes, such as superficial spreading melanoma, which are more prone to occur at sites with acute intermittent sun damage. In summary, molecular alterations in cutaneous neoplasms of the head and neck are often related to UV exposure. Their molecular footprint often reflects the histologic tumor type, and familiarity with these changes will be increasingly necessary for diagnostic and therapeutic considerations.

Relation between expression pattern of p53 and survivin in cutaneous basal cell carcinomas

Background

The tumor suppressor gene p53 is a key regulator of cell division and/or apoptosis. Survivin is a multifunctional member of the inhibitor of apoptosis family. Survivin and p53 represent diametrically opposed signals that influence the apoptotic pathway.

Material/Methods

To determine the role of p53 and survivin in basal cell carcinoma (BCC), we evaluated the expression pattern of both proteins with regard to the percentage of positively immunostained tumor cells, the intensity of staining, and subcellular localization among 31 subjects with BCC.

Results

Overexpression of p53 protein was found in 28 of 31 cases (90.3%), whereas survivin accumulation was seen in 27 (87.1%). For p53, moderate and/or strong immunoreactivity was seen in 20 of 28 cases (71.4%), and 26 of 28 cases (92.9%) showed more than 25% reactive tumor cells. Nuclear p53 staining was detected in 23 of 28 cases (82.1%), whereas combined nuclear and cytoplasmic localization was found in only 5 of 28 cases (17.9%). Survivin revealed mild intensity of immuno-reaction in 22 of 27 cases (71%), and 25 of 27 cases (92.6%) showed less than 25% labeled tumor cells. Combined nuclear and cytoplasmic survivin localization was present in 26 of 27 cases (96.3%). Statistically significant differences were detected in the assessed expression parameters between those proteins.

Conclusions

Our results suggest that overexpression of wild type p53 protein may suppress the expression of survivin and its antiapoptotic activity in BCC cells.

Single base instability is promoted in vulvar lichen sclerosus

Single base substitution mutations in codons 248 and 273 of TP53 and codon 12 Kirsten-ras (KRAS) are commonly found in human carcinomas. To determine whether these mutations also occur in normal and inflamed tissues from which carcinomas arise, we utilized the ultra-sensitive polymerase chain reaction/restriction endonuclease/ligase chain reaction mutation assay. Ninety samples of genital skin, including lichen sclerosus (LS) affected skin, adjacent normal and non-adjacent normal, were assayed. Mutations were detected in 103 of 349 assays and consisted of KRAS G34A, G34T, G35A, and TP53 C742T, G818C, C817T, and G818A mutations. Mutant prevalence varied from 1 to 20 per 10(6) wild-type cells. Mutations occurred significantly more frequently in LS (78/224 (35%)) than adjacent normal (20/88 (23%)) and non-adjacent normal genital skin (5/38 (13%)). KRAS G34A mutation was relatively common to all classes of specimen, whereas TP53 gene C742T and G818C mutations were significantly more frequent in LS than normal genital skin. In matched samples, immunohistochemistry evaluation of p53 protein expression revealed the presence of epidermal p53 clones in LS whose presence and number significantly correlated with the presence of TP53 C742T and G818C mutations. Based on these results, it appears oncogenic point mutations occur in normal genital skin, and are selected for in LS.

Early cancers of the skin: clinical, histopathological, and molecular characteristics

Because skin lesions are visible and easily accessible, skin cancers provide us with an excellent in vivo model to study the development of cancers. Cutaneous malignant melanoma and squamous cell carcinoma (SCC) both arise from the epidermis and have an initial progression stage in which proliferation of the neoplastic cells is confined to the epidermis. This stage is called melanoma in situ or SCC in situ. Molecular analyses of melanoma in situ and of solar keratosis, a prototype of early SCC in situ, show that loss of p16(INK4a)/p14(ARF) and dysfunction of p53 play a critical role, respectively. Furthermore, there seems to be potential precursor cells to these in situ lesions, which are not discernible with conventional hematoxylin and eosin-stained sections. The precursor cells have minimal but critical genetic alterations, such as cyclin D1 amplification and p53 mutation, and can be identified using fluorescent in situ hybridization and immunostaining with p53 antibodies, respectively. These precursor cells may be defective in repair response to DNA damage, and would have proliferative or survival advantages over their normal neighboring counterparts in the presence of growth factor stimulation or genotoxic events, such as ultraviolet irradiation. Such precursor clones may be induced at a rather young age, and their number and size increase with accumulating carcinogenic stimuli. If these lesions acquire additional mutations, they could progress to clinically visible lesions of in situ carcinoma. Precise molecular analyses of early stages of skin cancers may have a strong impact on our understanding of in vivo development of cancers in other human organs.

Nuclear Morphometry and Molecular Biomarkers of Actinic Keratosis, Sun-Damaged, and Nonexposed Skin

Computer-assisted image analysis is useful for quantifying the histologic and molecular changes of sun-induced squamous cell carcinoma progression. We used the CAS 200 image analysis system to measure nuclear morphometric parameters, p53 expression, and proliferation markers in actinic keratosis (AK), sun-exposed, and normal skin in 51 patients. Nuclear morphometry revealed significant increases in nuclear absorbance, irregularity of nuclear shape, and nuclear size in AK compared with normal and sun-damaged skin. These parameters showed significantly greater variability in AK nuclei. Argyrophyllic nucleolar organizer area and number were also significantly greater in AK compared with sun-damaged skin and normal skin. Ki67 and p53 expressions were both increased in sun-damaged skin relative to normal and greater still in AK. These data are evidence that sun damage induces proliferation and p53 abnormalities before the appearance of nuclear abnormalities and their associated DNA instability. Following these changes during a skin cancer chemopreventative trial can then help assess the efficacy of the agent and help determine where in the progression of neoplastic changes it exerts its biological effects.

No evidence of deregulated patched-hedgehog signaling pathway in trichoblastomas and other tumors arising within nevus sebaceous

Nevus sebaceous is a congenital malformation of the skin within which a number of neoplasms showing adnexal differentiation may arise. Recently, deletions in the patched gene region were reported in nevus sebaceous and constitutive activation of the patched-hedgehog signaling pathway was implicated in the development of tumors arising within nevus sebaceous. To substantiate further a role of the patched-hedgehog signaling pathway in secondary tumors arising within nevus sebaceous, we examined 11 nevus sebaceous associated with secondary tumors for loss of heterozygosity of the patched gene region by microsatellite polymerase chain reaction and patched mRNA expression by in situ hybridization. Unexpectedly, however, none of the tumors (including eight trichoblastomas) and nevus sebaceous lesions showed loss of heterozygosity at any polymorphic loci close to the patched gene. Further more, none of the nevus sebaceous lesions and secondary tumors gave detectable signals for patched mRNA. In contrast, four of 11 sporadic basal cell carcinomas, that were examined for comparison, showed loss of heterozygosity at the patched gene locus (p <0.05), and moderate to strong signals for patched mRNA was observed in all seven basal cell carcinoma tumors examined (p <0.0001). Additional investigation by reverse transcription-polymerase chain reaction in four basal cell carcinomas and two nevus sebaceous tumors also showed the expression of Gli-1, another target gene in the patched-hedgehog signaling pathway, in all the basal cell carcinomas samples but not in any of the nevus sebaceous tumors examined. The findings in this study do not support the view that the deregulation of the patched-hedgehog signaling pathway is involved in the pathogenesis of nevus sebaceous and associated tumors, and show that, although morphologically similar, trichoblastomas and basal cell carcinomas have a different molecular pathogenesis.

PATCHED and p53 gene alterations in sporadic and hereditary basal cell cancer

It is widely accepted that disruption of the hedgehog-patched pathway is a key event in development of basal cell cancer. In addition to patched gene alterations, p53 gene mutations are also frequent in basal cell cancer. We determined loss of heterozygosity in the patched and p53 loci as well as sequencing the p53 gene in tumors both from sporadic and hereditary cases. A total of 70 microdissected samples from tumor and adjacent skin were subjected to PCR followed by fragment analysis and DNA sequencing. We found allelic loss in the patched locus in 6/8 sporadic basal cell cancer and 17/19 hereditary tumors. All sporadic and 7/20 hereditary tumors showed p53 gene mutations. Loss of heterozygosity in the p53 locus was rare in both groups. The p53 mutations detected in hereditary tumors included rare single nucleotide deletions and unusual double-base substitutions compared to the typical ultraviolet light induced missense mutations found in sporadic tumors. Careful microdissection of individual tumors revealed genetically linked subclones with different p53 and/or patched genotype providing an insight on time sequence of genetic events. The high frequency and co-existence of genetic alterations in the patched and p53 genes suggest that both these genes are important in the development of basal cell cancer.

Persistent p53 mutations in single cells from normal human skin

Epidermal clones of p53-mutated keratinocytes are abundant in chronically sun-exposed skin and may play an important role in early development of skin cancer. Advanced laser capture microdissection enables genetic analysis of targeted cells from tissue sections without contamination from neighboring cells. In this study p53 gene mutations were characterized in single cells from normal, chronically sun-exposed skin. Biopsies were obtained from skin subjected to daily summer sun and skin totally protected from the sun by blue denim fabric. Using laser capture microdissection, 172 single-cell samples were retrieved from four biopsies and analyzed using single-cell polymerase chain reaction and direct DNA sequencing. A total of 14 different mutations were identified in 26 of 99 keratinocytes from which the p53 gene could be amplified. Mutations displayed a typical UV signature and were detected in both scattered keratinocytes and in a small cluster of p53-immunoreactive keratinocytes. This minute epidermal p53 clone had a diameter of 10 to 15 basal cells. Two missense mutations were found in all layers of epidermis within the p53 clone. The presented data show that p53 mutations are common in normal skin and that a clone of keratinocytes with a mutated p53 gene prevailed despite 2 months of total protection from ultraviolet light.

High frequency of loss of heterozygosity on chromosome region 9p21-p22 but lack of p16INK4a/p19ARF mutations in greek patients with basal cell carcinoma of the skin

Basal cell carcinoma of the skin is the most common neoplasia in humans. Previous studies have shown the existence of allelic imbalance (loss of heterozygosity and microsatellite instability) in BCC on several human chromosomes. Chromosome region 9p21-p22 harbors the CDKN2a/p16INK4a, p19ARF, and p15INK4b tumor suppressor genes. To determine the contribution of these genes to the development of basal cell carcinomas we looked for evidence of allelic imbalance in 67 sporadic basal cell carcinoma specimens from Greek patients and screened 28 of them presenting loss of heterozygosity at 9p21-p22 for germline mutations in p16INK4a and p19ARF genes. Chromosome regions 17q21 and 17p13 were also screened for allelic imbalance in all the 67 basal cell carcinoma specimens. Overall, 69% (46 of 67) of the specimens displayed loss of heterozygosity in at least one microsatellite marker, whereas only six of the 67 (9%) exhibited microsatellite instability. For the 9p21-p22 locus the overall frequency of loss of heterozygosity reached 55% (37 of 67) and is the highest reported. The overall frequency of loss of heterozygosity for the 17q21 locus is 34% (22 of 64) and for the 17p13 locus is 11% (seven of 65). Two of the 28 loss of heterozygosity positive cases were heterozygous for a previously described polymorphism, Ala148Thr, in exon 2 of the CDKN2a gene. This is the first demonstration of polymorphism in the CDKN2a gene in human basal cell carcinomas. No sequence variation in exon 1beta of the p19ARF gene was found. Our results provide evidence of a significantly high occurrence of loss of heterozygosity for the 9p21-p22 locus; however, lack of p16INK4a/p19ARF mutation suggests that these genes seem not to be implicated by mutational inactivation in the development of basal cell carcinoma. Other(s), yet unidentified, tumor suppressor gene(s) located in this locus may be related to this specific type of skin cancer.