Postradiation neural sheath sarcoma of the brachial plexus: a case report.

Sarcoma arising in the brachial plexus is a rare complication following radiation therapy, with only 7 patients reported in the literature. The absolute number of patients is likely to increase with the growth of radiation therapy to treat breast cancer. Because of its rarity, early diagnosis requires a high degree of suspicion. We present a patient with neural sheath sarcoma of the brachial plexus arising 18 years after external beam radiation for breast cancer. The interval between presentation and definitive therapy was prolonged by workup and treatment of carpal tunnel syndrome and cervical nerve root compression. The English language literature regarding postradiation sarcoma is reviewed and the clinical, radiological, and electrophysiological workup of postradiation brachial plexopathy is discussed.

Restoration of CDKN2A into melanoma cells induces morphologic changes and reduction in growth rate but not anchorage-independent growth reversal.

CDKN2A is a melanoma susceptibility gene that is mutated and/or deleted in familial and sporadic melanoma as well as in a range of other tumors. It encodes a cell cycle regulator, p16, whose function is to inhibit activity of cyclin-dependent kinases 4 and 6. We set out to investigate the effect of reintroducing CDKN2A into MM96L, a melanoma cell line that does not express p16, by electroporation of wt CDKN2A cDNA. Our results show that transfection of the CDKN2A cDNA has a dramatic effect on cell morphology, inducing a more dendritic phenotype resembling that of adult melanocytes. This effect on cell morphology was not cell line specific because it was reproduced in another melanoma line (SK-MEL-13), which has a homozygous deletion of CDKN2A. It was abolished by mutations that abrogate p16 function, as shown by transfection of a Pro81Leu p16 variant. Reintroduction of levels of p16 protein similar to those of cultured neonatal foreskin melanocytes decreased the growth rate of the transfected clones. Surprisingly, we did not see any effect on anchorage-independent growth or on the following melanoma markers tested by western blotting: p21/WAF1, tyrosinase-related antigen 1, HMB45, and intermediate filament antigen. These data indicate that reintroduction into melanoma cells of wild type p16 at levels similar to cultured melanocytes can induce morphologic changes and suppress growth but is not sufficient to affect anchorage-independent growth.

Mutations of the p16 gene product are rare in prostate cancer.

BACKGROUND: The p16 gene product is a negative regulator of cell cycle and has been shown to be deleted or mutated in a number of tumor cell lines and primary tumors. The role of p16 in prostate cancer is not defined. Prostate cancer tissues and cell lines were evaluated for p16 gene alterations. METHODS: Five metastatic prostate cancer cell lines were analyzed for p16 gene structure and its expression by Southern and Northern blot analyses. Forty-one DNA specimens from 18 microdissected primary tumor specimens, adjacent normal tissues, and cell lines were amplified by polymerase chain reaction for p16 protein coding and splice junction sequences. Mutations were analyzed by single strand conformation polymorphism and DNA sequencing. RESULTS: DU 145 cell line exhibited a missense mutation in codon 84 (GAC to TAC). With the exception of previously reported polymorphism, no mutation was detected in p16 coding or splice junction sequences in primary prostate cancer specimens. CONCLUSIONS: Inactivation of p16 gene by mutations in the protein coding sequence does not play a major role in the genesis of primary prostate cancer.

Increased risk of pancreatic cancer in melanoma-prone kindreds with p16INK4 mutations.

BACKGROUND: A gene on chromosome 9p, p16INK4, has been implicated in the pathogenesis of cutaneous malignant melanoma in 19 melanoma-prone families. In 10 of these kindreds mutations that impaired the function of the p16INK4 protein (p16M alleles) cosegregated with the disease. By contrast, in the other nine kindreds the mutation did not alter the function of p16INK4 (p16W alleles). We looked for differences in clinical and genetic epidemiologic features in these two groups of families. METHODS: We compared the median ages at diagnosis of melanoma, number of melanomas, thickness of the tumors, and number of nevi in the kindreds. We estimated prospectively the risks of melanoma or other cancers in families followed for 6 to 18 years and the risks of other cancers since 1925 (the entire period) by comparing the number of cancer cases observed with the number expected. RESULTS: The risk of invasive melanoma was increased by a factor of 75 in kindreds with p16M alleles and a factor of 38 in kindreds with p16W alleles. Although this difference was not significant (P = 0.14), there was a striking difference in the risk of other tumors. In kindreds with p16M alleles, the risk of pancreatic cancer was increased by a factor of 13 in the prospective period (2 cases observed, 0.15 expected; standardized incidence ratio, 13.1; 95 percent confidence interval, 1.5 to 47.4) and by a factor of 22 in the entire period (7 cases observed, 0.32 expected; standardized incidence ratio, 21.8; 95 percent confidence interval, 8.7 to 44.8). In contrast, we found no cases of pancreatic cancer in kindred with p16W alleles. CONCLUSIONS: The development of pancreatic cancer in kindreds prone to melanoma may require a p16M mutation. Genetic factors, such as the kind of mutation found in p16INK4, may explain the inconsistent occurrence of other cancers in these kindreds.

Mutations of the CDKN2/p16INK4 gene in Australian melanoma kindreds.

The cyclin dependent kinase inhibitor 2 (CDKN2) gene on chromosome 9p21 is potentially involved in the genesis of many cancers and is currently under intense investigation as a possible melanoma susceptibility locus. We have analyzed 18 Australian melanoma kindreds for mutations within the coding and neighboring splice junction portions of the CDKN2 gene. In seven kindreds (including our six largest), CDKN2 mutations were found to segregate with the putative melanoma chromosome previously assigned by 9p haplotype analysis. These changes included the duplication of a 24 bp repeat, a deleted C residue resulting in the introduction of a premature stop codon, and four single basepair changes causing amino acid substitutions. Mutations segregated to 46 of 51 affected individuals in these seven kindreds, with three apparent sporadic cases in one family and one in each of another two families. Penetrance was variable (55-100%) among the different mutations. These data provide additional strong support that the CDKN2 gene is the chromosome 9p21 familial melanoma locus.

Mutations associated with familial melanoma impair p16INK4 function.

Cell division is controlled by a series of positive and negative regulators which act at sequential points throughout the cell cycle. Disturbance of these checks could contribute to cancer by allowing excessive cell proliferation. The point in G1 at which cells irrevocably commit to DNA synthesis is controlled by protein complexes consisting of cyclin-dependent kinases (CDK4 or CDK6) and cyclins (D1, D2 or D3). These complexes are inhibited by low molecular weight proteins, such as p16INK4 (refs 1,2), p15INK4B (ref. 3) and p18 (ref. 4). Deletion or mutation of these CDK-inhibitors could lead to unchecked cell growth, suggesting that members of the p16INK4 family may be tumour suppressor genes. The recent detection of p16INK4 (MTS1) mutations in familial melanoma kindreds, many human tumour cell lines, and primary tumours is consistent with this idea. Previously, we described eight germline p16INK4 substitutions in 18 familial melanoma kindreds. Genetic analyses suggested that five mutations predisposed carriers to melanoma, whereas two missense mutations had no phenotypic effect. We now describe biochemical analyses of the missense germline mutations and a single somatic mutation detected in these families. Only the melanoma-predisposing mutants were impaired in their ability to inhibit the catalytic activity of the cyclin D1/CDK4 and cyclin D1/CDK6 complexes in vitro. Our data provide a biochemical rationale for the hypothesis that carriers of certain p16INK4 mutations are at increased risk of developing melanoma.

Germline p16 mutations in familial melanoma.

The p16 gene is located in chromosome 9p21, a region that is linked to familial melanoma and homozygously deleted in many tumour cell lines. We describe eight p16 germline substitutions (one nonsense, one splice donor site and six missense) in 13/18 familial melanoma kindreds. Six of these mutations were identified in 33/36 melanoma cases in nine families, whereas two were detected in normal controls and are not disease-related. The melanoma-specific mutations were detected in 9p21-linked, but not in 1p36-linked, families, thereby confirming previous reports of genetic heterogeneity. Functional analyses of these mutations will confirm those causally related to the development of familial melanoma.