Forty-five of 53 (85%) specimens from a range of primary and metastatic melanomas were found to have detectable evidence of p53 gene mutation, by virtue of the immunohistochemical detection of mutant p53 protein.
A replication-deficient adenovirus (Ad) vector which carries the cDNA for wild-type p53 (AdCMV.p53) was tested for its in vitro and in vivo effects on the growth of murine melanoma cell line B16-G3.26 and human melanoma cell line SK-MEL-24.
Altogether, N-ras p21 alterations are registered at earlier stages than p53 alterations in melanoma development and may be of aetiological importance, whereas p53 alterations may be associated with tumour progression in the late stages.(ABSTRACT TRUNCATED AT 250 WORDS)
As p53 gene mutations occur infrequently in malignant melanoma, other mechanisms are proposed to influence p53 protein expression in melanocytic lesions.
Some bladder primary tumors and some bladder and melanoma tumor cell lines contain mutations in both P16 and P53 at frequencies that suggest that p53 and p16 function in different pathways, each of which is important in suppressing malignant transformation.
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.
No sequence alterations of the p53 gene were detected in either the melanoma or nasopharyngeal tumours and only 19% of the primary breast carcinomas showed a variant band indicative of a mutation.
Our results, together with other findings at the DNA level, suggest that the p53 gene appears not to be commonly involved in the development of melanoma, at least by its most frequent mechanisms of deletion of one allele and/or mutation in the other.
These data suggest that overexpression of the p53 gene product is a late event in the progression of melanoma and consequently indicate that expression of this protein cannot be used as a marker to identify patients at high risk for the subsequent development of melanoma.
These results are consistent with there being no association between p53 overexpression in thin melanomas and risk of metastasis, however, the sample size was small, and the existence of such an association cannot beruled out with confidence.
The differences in p53 immunohistological expression between cutaneous melanomas and Spitz naevi suggest that alterations of the protein may be important in the pathogenesis of the tumour.
We believe that the immunohistochemical detection of p53 protein with the use of monoclonal antibodies such as BP53-12 on paraffin sections, especially when strong nuclear reactivity is demonstrated, may prove to be an adjunctive tool in the histopathologic differentiation of MM from SN.
Abnormalities of p53 expression occur rarely in cutaneous melanomas, but overexpression of p53 may occur in a subset of melanomas with a high index of proliferation.
Immunohistochemical analysis with a monoclonal antibody was used to determine whether alterations of p53 were present in 35 enucleated archival uveal melanomas.
Our results suggest that a) p53 gene mutations are a rare event in human melanoma; b) accumulation and thus immunohistochemically detectable expression of p53 may result from posttranslational mechanisms affecting the p53 gene product; and c) p53 and mdm-2 are more important in late events in melanoma carcinogenesis.
The level of immunohistochemical expression of p53 is low in primary skin melanoma, and it is not valuable as a general prognostic marker for this tumor. p53 expression is not associated with melanoma thickness, indicating that high p53 expression is not a late phenomenon in the progression of this tumor.