Background: Carcinoma of the breast during pregnancy represents 2-5% of all breast cancers. The frequency and histopathologic spectrum of breast cancer are similar in pregnant and nonpregnant women. Infiltrating lobular carcinoma is one of the less understood types of breast cancer, and its metastatic pattern seems to be different from that of infiltrating ductal carcinoma. Breast neoplasms rarely present as cancer from an unknown primary site.
Case: A woman in the third trimester of pregnancy developed carcinoma massively metastatic to the bone marrow and liver from an unknown primary tumor. At 32 weeks' gestation a healthy male was delivered by cesarean section. The patient died 12 hours after delivery. The autopsy revealed an infiltrating lobular carcinoma, 1.5 cm, of the breast.
Conclusion: Massive metastases from an occult lobular breast carcinoma in a pregnant woman are very rare. Diffuse metastatic spread, which often complicates or delays the diagnosis, is a characteristic pattern of infiltrating lobular carcinoma. Cancer from an unknown primary site during pregnancy is an exceptional finding. If a metastatic adenocarcinoma is diagnosed in a pregnant woman, a breast primary should be strongly suspected.