Metastatic malignancies of unknown primary origin is the 8th most common form of malignancy accounting for 0.5% to 3.5% of all malignant solid tumors. It is estimated that 10-15% of oncology patients have a tumor of unknown primary origin. Fine needle aspiration and effusion cytologies have assumed a pivotal role for the diagnosis of metastatic disease and often represent the initial procedures in the work-up of these cases. In addition to establishing a definitive diagnosis of metastasis, pathologists are increasingly asked to determine the primary site. This task can be especially challenging if there is no previous history of malignancy, prior pathology is not available for review, or there is an unpredictable pattern of metastasis. In this short course we will present a contemporary clinicopathologic approach for the work-up of metastatic disease of unknown primary site that includes cytomorphology, ancillary studies and clinicopathologic correlation including recognition of common and unusual patterns of metastasis. The cytologic subclassification of malignancies into morphologic categories such as clear cell, oncocytic, spindle, small cell, and large pleomorphic cells will be emphasized as well as conventional histologic/cytologic considerations and the potential pitfalls in diagnosis when look-alikes are encountered. In addition, the selective use of ancillary studies such as molecular diagnostics, electron microscopy and especially immunohistochemistry will be discussed as an aid in determining cell lineage and site of origin. Although pathologists may be familiar with the more usual patterns of metastasis to sites such as lung, liver and lymph nodes, cancer may occasionally metastasize to unusual or uncommon sites such as breast, spleen, pancreas and thyroid. This unpredictable pattern of metastasis may pose a diagnostic problem for both clinicians and pathologists and can potentially result in an erroneous cytologic diagnosis of a primary malignancy arising in these sites. Familiarity with the variable patterns of metastasis and primaries most commonly associated with those metastatic sites is crucial in narrowing down the possible origins of these neoplasms. We will also discuss the cost-effectiveness of the cytologic work-up of metastases of unknown origin, and how oncologists may better use the pathologic information to direct their management, especially when favorable types of malignancies are identified that are more responsive to treatment. A case-study approach will be adopted.

This course is suitable for residents as well as practicing pathologists. A set of transparency slides and a slide key will be mailed to registrants prior to the meeting. A course syllabus will be distributed at the time of the course.

(Last scheduled presentation)