Familial breast cancers without mutations in BRCA1 or BRCA2 have low cyclin E and high cyclin D1 in contrast to cancers in BRCA mutation carriers.

Purpose: We analyzed the expression of critical cell cycle regulators cyclin E and cyclin D1 in familial breast cancer, focusing on BRCA mutation-negative tumors. Cyclin E expression in tumors of BRCA1 or BRCA2 carriers is higher, and cyclin D1 expression lower, than in sporadic tumors. In familial non-BRCA1/2 tumors, cyclin E and cyclin D1 expression has not been studied.

Experimental Design: Cyclin E and cyclin D1 immunohistochemical expression was studied in tissue microarrays consisting of 53 BRCA1, 58 BRCA2, 798 familial non-BRCA1/2, and 439 sporadic breast tumors.

Results: In univariate analysis, BRCA1 tumors had significantly more frequently high cyclin E (88%) and low cyclin D1 (84%) expression than sporadic (54% and 49%, respectively) or familial non-BRCA1/2 (38% and 45%, respectively) tumors. BRCA2 tumors had significantly more frequently low cyclin D1 expression (68%) than sporadic or familial non-BRCA1/2 tumors and significantly more frequently high cyclin E expression than familial non-BRCA1/2 tumors. In a logistic regression model, cyclin expression, early age of onset, and estrogen receptor (ER) and human epidermal growth factor receptor-2 (HER2) status were the independent factors most clearly distinguishing tumors of BRCA1 mutation carriers from other familial breast cancers. High cyclin E and low cyclin D1 expression were also independent predictors of BRCA2 mutation when compared with familial non-BRCA1/2 tumors. Most interestingly, lower frequency of high cyclin E expression independently distinguished familial non-BRCA1/2 tumors also from sporadic ones.

Conclusions: Cyclin E and cyclin D1 expression distinguishes non-BRCA1/2 tumors from both sporadic and BRCA1- and BRCA2-associated tumors and may reflect different predisposition and pathogenesis in these groups.