Clinical and histopathological features of patients with metastatic solid tumor of unknown origin in bone marrow: an eight-year follow-up study

Metastasis represents the main cause of cancer-related death. A minority of patients were firstly diagnosed with solid tumor of unknown origin in bone marrow (BM-STUOs) before the appearance of clinical symptoms. We carried out an eight-year follow-up study for 94 patients (66 men and 28 women) with BM-STUOs. The median age of patients enrolled in this research was 58 years. Most of them (79, 84.0%) complained dizziness or fatigue. Fifty-four patients (57.4%) were admitted to their neighborhood hospital with local or widespread bone pain. Anemia (29.8%), thrombocytopenia (13.5%) and pancytopenia (9.0%) were the most common laboratory findings. To gain more insights into the lesions, bone marrow biopsy was undertaken. Histologically, malignant cells were arranged in clusters and surrounded by fibroblasts. Osteogenic and osteoclastic reactions were obvious. However, the primary sites of these metastatic lesions are always obscure because of the lack of histological evidence. A panel of immunohistochemical antibodies was employed to identify the phenotype of tumor cells. Unfortunately, definite diagnosis was established in only 48 patients. Kaplan-Meier analysis indicated that the prognosis of patients with definite origin was better than the patients without (P<0.05). Furthermore, the time consumption of diagnosis will affect the survival of patients with BM-STUOs.