Multiple myeloma presenting as anaplastic carcinoma. The role of electron microscopy in the diagnosis.

A tumor excised from the ninth right rib of a patient with chest pains was diagnosed independently by two pathologists as anaplastic carcinoma. Light microscopy of the tumor cells found in the sternal bone aspiration biopsy did not contribute to the diagnosis. When the cells were examined with a transmission electron microscope, the diagnosis of multiple myeloma was established and proved by suitable laboratory tests. Following treatment according to the M2 protocol, the patient is presently in an excellent condition. This case indicates that the electron microscope may serve as an important tool for the diagnosis of diseases difficult to clarify with the light microscope.