CHROMOSOME 9P ALLELIC LOSS AND P16 CDKN2 IN BREAST-CANCER AND EVIDENCE OF P16 INACTIVATION IN IMMORTAL BREAST EPITHELIAL-CELLS/

To define the extent of involvement of chromosome 9p in breast carcino genesis, we performed microsatellite length polymorphism analysis of m arkers spanning this region. Of 24 primary breast carcinomas analyzed, we observed a high frequency (58%) of loss of heterozygosity or allel ic imbalance affecting subregion 9p21-22. Mutational analysis of CDKN2 (p16) was performed to determine whether this gene was the target of such alterations. Of 21 tumors analyzed, only 1 showed a mutation of p robable consequence, suggesting that CDKN2 appears not to be the targe t of loss of heterozygosity and indicating the possible existence of a nother tumor suppressor gene within this region. Additionally, since i t has been suggested that some CDKN2 deletions and mutations could be due to an in vitro phenomenon, four immortal breast cell lines derived from normal epithelium, MCF10F, MCFI2F, 184A1, and 184B5, were examin ed for loss or mutation of CDKN2. Two lines (MCF10F and MCF12F) showed homozygous deletions of CDKN2, and one (184A1) revealed a hemizygous deletion and a nonsense mutation in the remaining allele. This could i mply an important role of CDKN2 in the control of immortalization or i n vitro adaptation and is the first evidence of such in nontumor-deriv ed cell lines. Additionally, this is the first report of frequent loss of heterozygosity in the 9p21-22 chromosome subregion of uncultured p rimary breast tumors.