An increased incidence of breast cancer is associated with which of the following?

An increased incidence of breast cancer is indeed associated with nulliparity, which refers to a woman who has never given birth. This relationship can be attributed to several factors related to hormonal exposure. Women who have not given birth tend to have an increased number of menstrual cycles in their lifetime, leading to prolonged exposure to estrogen and progesterone. This extended hormonal exposure has been linked to the proliferation of breast tissue and, consequently, a higher risk of developing breast cancer.

In contrast, other factors presented in the options provide different risk profiles. Late menarche, for example, generally results in fewer lifetime menstrual cycles, potentially lowering breast cancer risk. Trauma to the breast has not been conclusively associated with an increased risk of breast cancer, and early natural menopause actually reduces the overall exposure to ovarian hormones, which may lower the risk. Therefore, nulliparity stands out as a significant risk factor for breast cancer.