This chapter attempts to identify how pregnancy and lactation modify breast cancer risk, and highlights what can be regarded as state of the art in the diagnosis and treatment of pregnancy-associated breast cancer (PABC). It also considers the issue of preserving fertility during the treatment of breast cancer. The factor known to consistently decrease lifetime breast cancer risk regardless of ethnicity is early childbirth. An independent study found that breastfeeding decreased the risk of both hormone receptor-positive and hormone receptor-negative breast cancer. External beam radiation is an integral part of breast-conserving therapy and is, depending on the stage, also used after mastectomy. Women who want to conceive after breast cancer should receive individual counseling on prognosis with special attention to medical and psychosocial support. There may be a simple way of managing patients at risk of chemotherapy-induced infertility by deliberately producing a state of temporary, reversible medical castration during chemotherapy.