Effect of hypoxia and TP53 mutation status and cytogenetics of normal and malignant mammary epithelium.

It has been proposed that hypoxia favors the growth of tumor cells over normal cells, particularly tumor cells carrying TP53 mutations. Cytogenetic studies of breast cancer have shown that highly complex karyotypes seen in direct harvest preparations are rarely detected after short-term culture. In this study, 34 paired samples of breast carcinomas and grossly nontumorous tissue from the same breast were cultured at 20 and 5% (12 samples) or 20 and 0% oxygen (22 samples). Both carcinoma samples and nontumorous tissue survived at 0% oxygen. Recovery for 24 hours at 20% produced good yields for cytogenetic analysis. Lower oxygen levels did not specifically stimulate growth of tumor cells. Samples with TP53 mutations showed a consistently increased growth under anaerobic hypoxic conditions. Culture at 5% oxygen did not generally reveal more karyotypic abnormalities than found at 20%. In the samples cultured at 0 and 20%, karyotypic abnormalities were detected only in anaerobic hypoxic culture in two cases. Of the only four samples where more complex karyotypes were detected in the low-oxygen culture, two were TP53 mutated. Hypoxic treatment followed by recovery at 20% oxygen may thus increase the yield of complex karyotypes from a subset of breast carcinomas, particularly those with mutated TP53.

Cytogenetic changes in nonmalignant breast tissue.

Cytogenetic changes are common in breast cancer and have also been described in fibroadenomas and fibrocystic disease, but not in histologically normal breast tissue. Cytogenetic analysis was performed on nonmalignant breast tissue from benign breast lumps (n = 8), reduction mammoplasties (n = 31), and grossly nontumorous tissue from cancerous breasts (n = 84), using standard techniques and G-banding. All samples were reviewed histologically. Clonal chromosomal changes were found in three of eight benign breast tumors (38%). Of the reduction mammoplasties, 17 samples contained nonproliferative changes, and three of these (18%) showed a clonal deletion of 3p. No pathology was identified in the other 14 samples, of which one (7%) contained two clonal changes, apparently balanced translocations. Of nontumorous tissues from cancerous breasts, 15 (18%) showed clonal chromosomal abnormalities. Five of these samples were histologically normal. Two clones were identical to those found in the corresponding cancer. In 18 additional samples, single cells were detected with the same change as that seen in clones or single cells in the cancer. Only 4 of these 20 samples contained detectable cancer cells. Clonal abnormalities found in two or more samples included trisomies X, 7, and 20 and monosomies 19 and 18. Clonal changes were not significantly more frequent in proliferative than in nonproliferative lesions. The Icelandic BRCA2 founder mutation, 999del5, was detected in four samples, all histologically normal, two of which had clonal chromosomal abnormalities. In conclusion, clonal chromosomal changes are not infrequent in nonmalignant breast tissue and can be detected even in the absence of histological abnormalities.