Because more women are waiting to have children until later in life, cancer diagnoses in pregnancy are becoming more common. Gestational cancer is defined as a new cancer diagnosis during pregnancy or in the first year postpartum.1 The most common cancers in reproductive aged women are breast, melanoma, thyroid, cervical, and lymphomas, listed in order of decreasing frequency.2 The diagnosis of cancer in the gestational period poses many difficult decisions for which multiple clinical, personal, and ethical factors need to be considered for treatment planning. We review the pertinent information for some of the more common gestational cancers, as well as some less common, but with increasing prevalence in the United States.

BREAST CANCER

Gestational breast cancer is considered any breast cancer occurring either during pregnancy, in the year after delivery, or anytime during lactation. Breast cancer is one of the most common pregnancy-associated cancers. Pregnancy-associated breast cancer occurs in 20% of breast cancer patients younger than 30 years of age.3 The incidence is only 0.4% of all breast cancers diagnosed in women aged 16 to 49, however the rate is increasing.1 This increase is most likely secondary to delaying the age at which women begin childbearing. The majority of gestational breast cancer is infiltrating ductal carcinoma. Gestational breast cancer is more likely to be poorly differentiated and have metastases at the time of diagnosis when compared with nonpregnant women.4 There is typically a lower incidence of estrogen receptor–positive, progesterone receptor–positive breast cancer diagnosed during pregnancy and the postpartum period, whereas human epidermal growth factor 2–positive tumors seem to be equal in incidence to that of nonpregnant women.5 A diagnosis of breast cancer during pregnancy or lactation is often more challenging given the normal physiologic changes in the breast during these periods.6 For example, rapid enlargement and hypertrophy during pregnancy and the postpartum period can distort the anatomy of the breast. Often the diagnosis is delayed by pregnancy and lactation; hence, the diagnosis is made at more advanced stages during pregnancy.7 Interestingly, a breast cancer diagnosis during lactation can be detected by the milk rejection sign, in which the nursing infant will refuse to nurse from the cancerous side.2 Any breast mass persisting for more than 2 weeks during pregnancy or lactation needs to be evaluated. Even though 80% of breast biopsies during pregnancy are benign, delayed diagnosis because of pregnancy or lactation is critical to prognosis.