Primary Gastric Signet Ring Cell Carcinoma or Metastatic Lobular Carcinoma With Signet Ring Cells: A Diagnostic Challenge

Histologically, cells having vacuolated cytoplasm rich in mucin and pushing the nucleus to the periphery are indicative of signet ring cell carcinoma. This condition often affects the digestive system. On the other hand, it is a very uncommon subtype of invasive lobular breast carcinoma, with a higher probability (more than invasive breast carcinoma of no special type {IBC-NST}) to migrate to the stomach, spleen, urinary tract, and uterus.As with other metastatic carcinomas of breast origin, metastatic signet ring cell carcinoma of the breast is often treated with systemic therapies such as chemotherapy or hormonal therapy. However, surgical resection and eventual perioperative chemotherapy are usually recommended in case of primary gastric ring cell carcinomas that are non-metastatic. As a result, misdiagnosis might result in unneeded gastrectomy and chemotherapy, which would result in considerable mortality and morbidity.We report a case of mammary lobular carcinoma with signet ring cells metastatic to the stomach, a variant rarely described and challenging to distinguish from primary gastric signet ring carcinoma.