Bone marrow metastatic carcinoma. Light microscopy of a bone marrow smear. Signet-ring cell is a rare morphological finding in bone marrow ( lower half of image), which usually indicates metastatic carcinoma from either the gastrointestinal tract or a primary hematolymphoid neoplasm. The prognosis for bone marrow involvement with gastric adenocarcinoma is poor. Magnification 150 x when printed at 10 centimetres wide.