This study reports the cytopathologic diagnoses rendered on all malignant pleural effusions received and processed over a period of 14 years. Specimens of fluid from various body sites (25,464) were examined. Of these, 5888 (23%) were specimens of pleural effusions. Five hundred eighty-four specimens (9.9% of total pleural fluid specimens) taken from 472 patients were diagnosed as containing cancer cells. Of the malignant pleural effusions, 75.7% were classified as carcinomatous in type. Adenocarcinomas comprised 47.4% of the 584 specimens. The groups of large cell undifferentiated carcinoma and lymphoma/leukemia approximated one another in being the second most common cancer groups (14.3% and 15.0%, respectively). For both males and females, the frequency of organ site or primary tumor type was lung (35.6%), lymphoma/leukemia (15.9%), breast (14.8%), female genital tract (8.1%), and gastrointestinal tract (5.9%). Among male patients, the order of frequency was lung (49.1%), lymphoma/leukemia (21.1%), gastrointestinal tract (7.0%), genitourinary tract (6.0%), and malignant melanoma (1.4%). In female patients, the order of frequency was breast (37.4%), female genital tract (usually ovary) (20.3%), lung (15.0%), lymphoma/leukemia (8.0%), and gastrointestinal tract (4.3%). In 48 patients (10.2%) the primary site of neoplasm was never determined. In 90.5% of patients a cytopathologic diagnosis conclusive for cancer was obtained on the first specimen of fluid. There were no false positive diagnoses.

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Since its introduction as a screen for cervical cancer in the late 1940s, the Pap smear has become one of the most widely accepted screening procedures for cancer. Numerous scientific studies have now attested to its effectiveness. However, important issues related to the Pap smear, including cytologic nomenclature, accuracy, regulatory procedures, and screening guidelines, are still being evaluated and debated. This article provides an overview of important issues related to the Pap smear.