Inactivation of the CDKN2A and the p53 tumour suppressor genes in external genital carcinomas and their precursors.

BACKGROUND: p53 has been extensively studied in external genital carcinoma (EGC), and is frequently inactivated, but little is known about the role of the CDKN2A tumour suppressor gene in the oncogenesis of EGC. OBJECTIVES: To investigate the role of CDKN2A and p53 in the pathogenesis of EGCs and their precursor lesions vulval intraepithelial neoplasia (VIN3), penile intraepithelial neoplasia and lichen sclerosus (LS). METHODS: By means of CDKN2A and p53 mutation screening (single-strand conformational polymorphism analysis and sequencing), methylation analysis of alternative CDKN2A promoters (methylation-specific polymerase chain reaction) and p53 immununochemistry, we analysed eight invasive EGCs (five from vulva and three from penis) and 25 precancerous lesions (two undifferentiated VIN3 and 23 vulval/penile lesions of LS) from 33 patients. RESULTS: p53 mutations (mainly transversions) and CDKN2A mutations (including one hot spot) were present in 75% and 50% of invasive tumours, respectively, but were absent in all precancerous lesions. Remarkably, all CDKN2A-mutated tumours also harboured a p53 mutation. CDKN2A or p53 mutations were observed more frequently in LS-derived EGCs than in human papillomavirus-derived EGCs (P = 0.053). A positive anti-p53 staining, but without p53 mutations, was also detected in 30% of LS lesions, suggesting a p53 stabilization in response to inflammation and carcinogenic insult. Methylation of p16(INK4a) and p14(ARF) promoters was not a frequent mechanism of CDKN2A inactivation. CONCLUSIONS: Our study shows a high prevalence of co-inactivating mutations of p53 and/or CDKN2A genes in EGC, that seem to occur preferentially in LS-derived tumours and late in oncogenesis.

Germline and somatic mutations of the INK4a-ARF gene in a xeroderma pigmentosum group C patient.

Xeroderma pigmentosum is an inheritable autosomal recessive DNA repair deficient syndrome characterized by a high predisposition to skin cancers. An elevated proportion of tumors from xeroderma pigmentosum patients harbor ultraviolet-induced mutations (CC:GG > TT:AA tandem transitions) of the p53 and/or the INK4a-ARF genes. Here, we report the clinical and molecular features of a 12 y old xeroderma pigmentosum patient who, in addition to severe cutaneous clinical symptoms, also had three unusual tumors, a mediastinal lymphoblastic lymphoma, an atypical fibroxanthoma, and an epithelioid hemangioma. Single strand conformation polymorphism and sequencing analysis of the p53 and INK4a-ARF genes were carried out in DNA from normal skin and different tumors (four actinic keratosis, two microinvasive squamous cell carcinomas, one basal cell carcinoma, and one atypical fibroxanthoma) from the patient. After characterization of the xeroderma pigmentosum C complementation group, we found unexpectedly that this patient also carried a germline mutation of the INK4a-ARF locus affecting the p16INK4A reading frame. Three different somatic mutations that all harbor the signature of ultraviolet light (two of p16INK4A and one of p53) were also detected in the basal cell carcinoma. We hypothesize that the germline mutation of p16INK4A, in association with the nucleotide excision repair defect, could explain the patient's unusual phenotype. Furthermore, this study confirms that concomitant somatic mutations of INK4a-ARF and p53 occur in some xeroderma pigmentosum associated tumors, and seem to accumulate during tumor progression rather than the initiation step.

[An alternative to immunofluorescence on frozen tissue for the diagnosis of sub-epidermal auto-immune bullous dermatosis]. / Une alternative à l'immunofluorescence sur tissu congelé pour le diagnostic des dermatoses bulleuses auto-immunes sous-épidermiques.

The diagnosis of subepidermal auto-immune bullous dermatosis is usually based on immunofluorescence which demonstrates IgA, IgG, IgM or C3 on dermo-epidermal junction. However in some instance, this technique could not be performed. Here we report an alternative to immunofluorescence. It is a preembedding technique of immunolabelling using horseradish peroxidase, on fresh tissue without any freezing, before an inclusion in wax. So the observation of the labelling is possible with a standard microscope. This technique has been applied to 7 patients with various sub-epidermal auto-immune bullous dermatosis whose diagnosis was confirmed elsewhere by immunoelectron microscopy. It was as specific and sensitive than immunofluorescence whatever the bullous dermatosis.