Christopher R. Shea

Mutation and expression of the p53 gene in human malignant melanoma.

Derangement of the p53 tumor suppressor gene has been implicated in the aetiology of a wide range of human neoplasias. We have previously determined that overexpression and mutation of the p53 gene in cultured metastatic melanomas is low (11%). However, two recent immunohistochemical studies have reported that >85% of malignant melanoma specimens overexpress mutated p53 protein. In an effort to resolve this contradiction in the published literature, we have re-evaluated a range of cultured and non-cultured melanocytic lesions for the occurrence of point mutations in the p53 gene using DNA- and RNA-dependent single strand conformation polymorphism (RNA-SSCP) and direct DNA sequencing of polymerase chain reaction (PCR) amplified DNA, and overexpression of the p53 protein using immunohistochemistry. We found point mutations in 25% (9 of 36) of cultured melanomas and 0% in 34 fresh melanoma biopsies; however, increased p53 expression was found in 42% of paraffin-embedded melanoma specimens and 7% of benign lesions. The low frequency of p53 point mutations and high frequency of p53 expression suggests that derangement of the p53 gene by point mutations is not a common perturbation in the majority of melanoma cells, and that overexpression of p53 in this tumour type is due to a mechanism other than point mutation.

Regulation of global genome nucleotide excision repair by SIRT1 through xeroderma pigmentosum C

Disruption of the nucleotide excision repair (NER) pathway by mutations can cause xeroderma pigmentosum, a syndrome predisposing affected individuals to development of skin cancer. The xeroderma pigmentosum C (XPC) protein is essential for initiating global genome NER by recognizing the DNA lesion and recruiting downstream factors. Here we show that inhibition of the deacetylase and longevity factor SIRT1 impairs global genome NER through suppressing the transcription of XPC in a SIRT1 deacetylase-dependent manner. SIRT1 enhances XPC expression by reducing AKT-dependent nuclear localization of the transcription repressor of XPC. Finally, we show that SIRT1 levels are significantly reduced in human skin tumors from Caucasian patients, a population at highest risk. These findings suggest that SIRT1 acts as a tumor suppressor through its role in DNA repair.

Desmoplastic (sclerotic) nevus: an underrecognized entity that resembles dermatofibroma and desmoplastic melanoma.

Desmoplastic (sclerotic) nevus, a benign melanocytic neoplasm characterized by predominantly spindle-shaped nevus cells within a fibrotic stroma, can be confused with fibrous lesions and other melanocytic proliferations, including desmoplastic melanoma. We compared the histologic and immunohistochemical features of 16 desmoplastic nevi, nine desmoplastic melanomas, four hypopigmented blue nevi, and six dermatofibromas. The similarities between desmoplastic nevi and dermatofibromas included epidermal hyperplasia (12 of 16), presence of keloidal collagen (15 of 16), hypercellularity (16 of 16), and increased numbers of factor XIIIa-positive dendritic cells (12 of 12). The absence of adnexal induction (0 of 16), the rarity of lesions with multinucleated cells (3 of 16) or epidermal hyperpigmentation (2 of 16), and the presence of S-100 immunoreactivity (16 of 16) and melanocytic proliferation (9 of 16) helped differentiate desmoplastic nevi from dermatofibromas. The similarities between desmoplastic nevi and desmoplastic melanomas included the presence of atypical cells (16 of 16) and HMB-45 expression in the superficial portion of the lesions (11 of 16). The infrequent location on the head or neck (1 of 16), the absence of mitotic figures (0 of 16), a significantly lower number of Ki-67-reactive cells, and a decrease in HMB-45 expression in the deep area of the lesions (8 of 11) helped distinguish desmoplastic nevi from desmoplastic melanoma. Desmoplastic nevi had overlapping features with hypopigmented blue nevi, but features tending to favor the latter included a predominance of ovoid nuclei, higher numbers of atypical cells, and homogeneous staining with HMB-45. We conclude that a combination of histologic and immunohistochemical criteria facilitates the reliable diagnosis of desmoplastic nevus from its simulators.

Immunohistochemical expression of BCL-2 in melanomas and intradermal nevi

The BCL‐2 gene is the prototype of a newly described family of oncogenes involved in tumorigenesis by blocking apoptosis, or programmed cell death. Overexpression of BCL‐2 protein was originally described in follicular B‐cell lymphomas bearing the 14;18 translocation. BCL‐2 overexpression has also been described in other lymphomas and more rarely in neoplasms outside the lymphoid tissue. The aim of this paper is to determine the immunohistochemical expression of BCL‐2 in intradermal nevi and primary invasive and metastatic melanoma. Formalin‐fixed and paraffin‐embedded tissues from 4 cutaneous melanoma metastases, 10 primary invasive melanomas, and 10 intradermal melanocytic nevi were immimolabeled with monoclonal antibodies directed against BCL‐2 protein (Dako, clone 124) and Ki‐67 antigen (Amac, clone MIB‐1), after antigen retrieval techniques. Morphologically normal epidermal melanocytes expressed BCL‐2, as did nevi and melanomas in virtually all cells. However, whereas the labeling in normal melanocytes and nevus cells showed a uniformly strong reactivity, melanoma cells showed a variable but mainly weak reactivity. Ki‐67 antigen expression was restricted to melanomas. The widespread expression of BCL‐2 suggests that this onco‐protein cannot be involved in the malignant transformation of melanocytic cells. It seems likely that the decreased BCL‐2 expression detected in melanomas may reflect one further step of tumor progression in melanocytic neoplasms.

Correlating architectural disorder and cytologic atypia in clark (dysplastic) melanocytic nevi

Histological architecture is very important in the pathological diagnosis of Clark (also known as atypical or dysplastic) melanocytic nevi. However, few studies have attempted to quantify architectural features or to correlate them directly with cytology. In 166 consecutive Clark nevi, the presence or absence of the following features in the intraepidermal or junctional component was recorded: (1) Architecture: circumscription, symmetry, cohesiveness of nests, suprabasal melanocytes, confluence, and single-cell proliferation; (2) Cytology of melanocytes: round/euchromatic nuclei, nuclear enlargement, cell enlargement, and prominent nucleoli. Each criterion was given a value of 0 or 1, and a summation score was obtained for both architecture and cytology in each case. The chi-square test was used to determine the significance of relationships among these parameters. The degrees of architectural disorder and of cytologic atypia were positively correlated (P = .026). Scores for both parameters were distributed over a wide range of values and were concentrated toward the low-middle portion of the spectrum. Several particular architectural and cytologic variables showed significant interdependence. Clark nevi exhibit a broad spectrum of architectural disorder and cytologic atypia, which, according to our data, generally are closely related features. Because some cases displayed a relatively high score for one parameter but a low score for the other, quantification of both parameters permits a more complete histopathologic evaluation of these lesions and may provide additional information for their clinical management.

PTEN Positively Regulates UVB-Induced DNA Damage Repair

Nonmelanoma skin cancer is the most common cancer in the United States, where DNA-damaging ultraviolet B (UVB) radiation from the sun remains the major environmental risk factor. However, the critical genetic targets of UVB radiation are undefined. Here we show that attenuating PTEN in epidermal keratinocytes is a predisposing factor for UVB-induced skin carcinogenesis in mice. In skin papilloma and squamous cell carcinoma (SCC), levels of PTEN were reduced compared with skin lacking these lesions. Likewise, there was a reduction in PTEN levels in human premalignant actinic keratosis and malignant SCCs, supporting a key role for PTEN in human skin cancer formation and progression. PTEN downregulation impaired the capacity of global genomic nucleotide excision repair (GG-NER), a critical mechanism for removing UVB-induced mutagenic DNA lesions. In contrast to the response to ionizing radiation, PTEN downregulation prolonged UVB-induced growth arrest and increased the activation of the Chk1 DNA damage pathway in an AKT-independent manner, likely due to reduced DNA repair. PTEN loss also suppressed expression of the key GG-NER protein xeroderma pigmentosum C (XPC) through the AKT/p38 signaling axis. Reconstitution of XPC levels in PTEN-inhibited cells restored GG-NER capacity. Taken together, our findings define PTEN as an essential genomic gatekeeper in the skin through its ability to positively regulate XPC-dependent GG-NER following DNA damage.

Recurrent melanocytic nevus: A histologic and immunohistochemical evaluation

Background: Recurrent melanocytic lesions may histologically resemble malignant melanoma.

Immunohistochemistry of melanocytic proliferations

CONTEXT Histologic analysis allows accurate classification of most melanocytic lesions as benign or malignant. Only in a minority of lesions is it necessary to use other techniques as an aid in the diagnosis. Among them, most authors recommend immunohistochemistry. OBJECTIVE To describe how to apply immunohistochemistry to particular differential diagnoses and the potential pitfalls. DATA SOURCES Personal experience and review of literature. CONCLUSIONS There is no single marker, or combination thereof, that establishes an unequivocal diagnosis of melanoma or nevus. Thus it is necessary to carefully analyze the pattern of expression (patchy versus diffuse) and localization (maturation) in the context of morphologic standard features.

Molecular mechanisms of photodynamic therapy.

Despite its more than 100-year history in experimental and clinical use, photodynamic therapy (PDT) is only starting to be appreciated for its full potential. PDT combines a photosensitizer (PS) and light in the presence of oxygen to treat cancer and other disorders. This manuscript reviews molecular mechanisms that have been evaluated over the past years for the effects of PDT at the cellular level as well as in therapeutic settings in vivo. The availability of multiple PS with different structures and functional properties makes PDT an extremely versatile and, conversely, a challenging approach to cancer therapy. The advancing understanding of molecular pathways helps to design improved regimens. As most cancers are being treated with combination therapies, PDT is being integrated into rationally designed combined regimens that exploit molecular responses to PDT for improved efficacy.

Dysplastic naevi with moderate to severe histological dysplasia : a risk factor for melanoma

Background  The risk of malignant melanoma associated with histologically dysplastic naevi (HDN) has not been defined. While clinically atypical naevi appear to confer an independent risk of melanoma, no study has evaluated the extent to which HDN are predictive of melanoma.