Metastasis of unknown origin: the role of fine-needle aspiration cytology

Metastasis of unknown origin (MUO) manifests either as a tumor deposit in an organ, often cervical lymphadenopathy, or as a multiorgan carcinomatosis. As a diagnostic and therapeutic challenge, the definition of its cell type and possibly its origin is imperative, although a limited diagnostic investigation is usually recommended. At Hines VA Hospital from 1986 to 1994, there were 116 cases with admitting clinical diagnosis of MUO, evaluated by fine-needle aspiration cytology (FNAC). The ages of patients ranged from 29 to 82 years (mean 56 years). All were male; Caucasians predominated. The FNAC examination with Diff-Quik and Papanicolaou smears were complemented with special and immunostains in 48 cases (41%) and electron microscopy in 93 cases (80%). The FNAC involved lymph nodes in 57 cases (49%), liver in 27 cases (23%), skin in 22 cases (19%), bone in six cases (5%), lung in three cases (3%), and pleura in one case (1%). The neoplasm was generally cell typed, and there were 60 adenocarcinomas/poorly differentiated carcinomas, 26 small-cell carcinomas (SCC), 23 squamous-cell carcinomas (SQCC), and six undifferentiated large-cell carcinomas. The primary source was defined in 30 cases (26%), consisting of lung in 11 cases, prostate in nine, kidney in four, colon in four, pleura in one, and peritoneum in one. Clinical correlation also supported a lung origin for the SCC, while the majority of the SQCC in upper and middle cervical lymph nodes were considered head-and-neck tumors. Our results affirm that FNAC is a viable and simple procedure in MUO investigations.