The obtained data indicated that antimitotic effect of D-glucuronyl C5-epimerase in human breast cancer cells in vitro probably is realized mainly via the activation of tumour suppressor genes р53, BRCA1, SYK and E2F1 and change of a balance of pro- and anti-apoptotic factors BCL2, NFKB1 and TNF. The gene discussed is BRCA1; the disease is breast carcinoma.