Pregnancy-associated breast cancer (PABC) is defined as cancer of the breast diagnosed during pregnancy and up to 1 year postpartum. Delays in diagnosis are frequently associated with increased morbidity and mortality. The aim of this article is to determine the significance of early detection of PABC and to alert health care providers to include PABC in the differential diagnosis when evaluating a breast mass in the perinatal period. This integrative literature review evaluated 15 research studies by using the hypothetical deductive model of clinical reasoning to determine factors related to diagnosis of PABC. As women delay childbearing, the incidence of PABC increases with age. In the reviewed studies, breast cancer was diagnosed with greater frequency in the postpartum period than during any trimester in pregnancy. Delay in diagnosis is complicated by axillary lymph node metastasis, high-grade tumors at diagnosis, and poor outcomes. Early detection is a significant predictor of improved outcomes. Diagnostic modalities such as ultrasound, mammography, and biopsy can be safely used for diagnostic purposes in the evaluation of potential cases of PABC during pregnancy.