Breast cancer is among most common women's cancers at most parts of the world, and the incident is increasing among Iranian women. It seems that the age of disease development is lower in Iran compared to western countries. Breast cancer includes one third of the total female cancers and is the main factor for the major deaths caused by cancer at women 25-59 years old. Physiological changes during pregnancy makes the diagnosis difficult, and with development of the pregnancy, diagnosis become harder. In case the disease is suspected, appropriate interventions must be made as soon as possible. Mammography is permitted at this period. On tumor diagnosis, with attention to results of several researches, sonography is more sensitive at pregnancy and breastfeeding. This study was designed in order to examine breast cancer during pregnancy. This is a review article and the resulting data are obtained through library and online researches.