The value of postmortem examination in cases of metastasis of unknown origin—20-year retrospective data from a tertiary care center

BACKGROUND: Metastasis of unknown origin (MUO) is a diagnostic challenge in clinical practice even with the state of current advanced diagnostic technology. To evaluate the value of autopsy in determining the primary site of MUO, this study reviewed the Hamilton experience-over the last 20 years-with patients autopsied with clinical diagnosis of MUO. METHODS: All autopsy diagnoses from cases performed at the Hamilton Health Sciences Center and St Joseph's Healthcare from 1980 to 2000 were reviewed. Fifty-three cases of MUO were identified (MUO was defined as a patient with pathological and/or radiological diagnosis of a metastatic tumor for which the primary site of malignancy was unknown). The clinical history and gross and microscopic diagnoses for these cases were reviewed. RESULTS: There were 31 men (58.5%) and 22 women (41.5%) in the study. Their mean age was 66 years. Pathological diagnoses at autopsy were adenocarcinoma (n = 37), small cell carcinoma (n = 6), anaplastic carcinoma (n = 3), and undifferentiated carcinoma (n = 3). Primary tumors were identified in 27 patients (51%), most commonly in the lung (n = 8), large bowel (n = 6), and pancreas (n = 4). Histochemical and immunohistochemical stains were helpful in reaching the diagnosis of a primary tumor in 4 of 27 cases. CONCLUSIONS: The following were observed: (1) in this series, autopsy was helpful in establishing the diagnosis of a primary tumor in 51% of the cases, reaffirming the value of postmortem examination in these instances; (2) adenocarcinoma was the most frequent tumor presenting as MUO; (3) the lung and the large bowel were the most frequent sites for primary tumors; and (4) careful gross and histological examinations remain the most important tools in identifying the primary site.