The etiology, or cause, of any cancer is still unknown. Generally, it is believed that cancer develops when the genes responsible for malignant transformation (onkogenes) become active... or when the genes that prevent malignant transformation (anti-oncogenes) become inactive. Genetic mutations activate or de-activate certain genes. Mutations can be provoked by various factors, many of them unknown. In the case of breast cancer, it is believed that the hyper-stimulation of estrogen hormones is responsible for malignant transformation rather than the chemicals found in some creams.
You may consult a dermatologist about the hairs on your nipples.