Malignant pleural effusions due to small-cell lung carcinoma: A cytologic and immunocytochemical study

Patients with small-cell lung carcinoma (SCLC) rarely present with pleural effusions. Based on morphology alone, recognition of SCLC in effusion cytol ogy may be challenging because of the resemblance of neoplastic cells to ly mphocytes. Immunocytochemistry may be helpful in its diagnosis. The objecti ve of this study was to review the morphology and evaluate the use of immun ochemistry in diagnosing SCLC in pleural fluids. Patients with SCLC who pre sented with pleural effusions were identified during a 6-yr period. The cyt ology and medical records were reviewed. Formalin-fixed, paraffin-embedded cell blocks of fluid specimens were immunostained with neuroendocrine marke rs (chromogranin A and synatophysin), cytokeratin 20 (CK20), and thyroid tr anscription factor-1 (TTF-1). The latter is a nuclear transcription protein that is expressed in normal respiratory, epithelium and also in more than 90% of SCLCs. Of the 256 patients diagnosed with SCLC during the study peri od, 8 (2.7%) patients (3 females and 4 males, age range from 56-85 yr) also developed pleural effusions. One patient had 2 fluid specimens daring the course of their disease, giving a total of 9 specimens. Four specimens had a positive cytologic diagnosis of SCLC, and 2 were initially diagnosed as s uspicious for SCLC The remaining 3 specimens were negative for SCLS. The sp ecimens with a positive or suspicious diagnosis showed single and aggregate s of small to medium-sized single cells with a high nuclearxytoplasinic (N: C) ratio, round to angulated nuclei, and salt-and-pepper chromatin. Nuclear molding was also noted. Five out of 6 (83%) specimens with a positive or s uspicious diagnosis of SCLC were positive for both chromogranin A and TTF-1 . Synaptophysin was positive in 3 of 6 (50%) positive or suspicious cases. None of the cases were positive for CK20. All cases with a negative cytolog ic diagnosis were negative for chromogranin A, synatophysin, CK20, and TTF- 1. In conclusion, patients with SCLC rarely present with pleural effusions. The cytology of SCLC is characteristic. The use of immunohistochemistry, p articularly, with antibodies to chromogranin A, TTF-1, and CK 20, aids in t he differential diagnosis. (C) 2001 Wiley-Liss, Inc.