Breast carcinoma diffusely metastatic to the spleen. A report of two cases presenting as idiopathic thrombocytopenic purpura.

Carcinoma metastatic to the spleen is found at autopsy in 6% to 13% of patients who die of cancer, yet clinical symptoms referable to splenic metastases are unusual. Two cases of breast carcinoma metastatic to the spleen discovered incidentally at therapeutic splenectomy for idiopathic thrombocytopenic purpura are described. On gross examination, the spleens were mildly enlarged with a homogeneous congested cut surface; rare 0.2-cm white nodules were present in one case. Microscopic examination revealed large, poorly cohesive cells that diffusely involved both the red and white pulp. Histochemical, immunohistochemical, and ultrastructural analyses confirmed the epithelial nature of the cellular infiltrate. These cases show that idiopathic thrombocytopenic purpura may herald the presence of diffuse splenic metastases when metastatic disease is not otherwise clinically suspected. The lack of a discrete tumor mass in the spleen in such cases may make the diagnosis of metastatic carcinoma a challenge both clinically and pathologically. Immunohistochemical and electron microscopic examinations are useful to establish the appropriate diagnosis in such cases.