Malignant Pleural effusion due to small cell carcinoma of lung, with a 3x2x2 cm lung mass
- loose aggregates as well as dispersed single cells
- cell size is small to intermediate with high N/C ratio, round to ovoid nuclei and scanty cytoplasm
- fine dispersed granular chromatin pattern
- no nucleoli
- Nuclear molding and crushing is seen
- background shows few dispersed lymphocytes, which are reactive in nature (compare it with cells of interest)
- occasional cell resembling the macrophages with engulfment of round cells are seen – phagocytic process
Points of Pathoclinics:
- effusion due to small cell carcinoma is uncommon and associated with decrease survival
- very close differentials are reactive lymphocytes, majority of low grade lymphoid neoplasm, carcinoid tumors, mesothelioma small cell type and poorly differentiated adenocarcinoma
- Close scrutiny of cell size, nucleus and chromatin pattern, nucleoli, amount of cytoplasm, dispersal of cells and molding/crushing pattern discriminate the small cell carcinoma from other differentials
- In difficult cases, useful stains are CD20, CD3, pankeratin (dot like pattern in small cell carcinoma) Synaptophysin, Chomogranin A, INSM1, CD56, TTF1 and P63
- High proliferation, apoptosis and necrosis are more in line with small cell carcinoma than carcinoid tumors
- CK7 and CK20 not much useful in differential diagnosis
- calretinin expression seen in approximately half of all cases of small cell carcinoma so use it with caution to differentiate mesothelioma from small cell carcinoma.
- Napsin A is negative in almost all cases of pulmonary small cell carcinoma so it is useful in combination with TTF1, to differentiate pulmonary small cell carcinoma from poorly differentiated lung adenocarcinoma.
- LBC shows more degenerative changes and dry artifact with exaggerated irregular nuclear shape and nuclear size variation and scanty cytoplasm than conventional smears.
Kim L, Choi SJ, Park IS, Han JY, Kim JM, Chu YC. Cytomorphologic features of small cell carcinoma of lung in effusion fluid using a liquid-based cytology technique. Diagn Cytopathol. 2020 Mar;48(3):203-210. doi: 10.1002/dc.24365. Epub 2019 Dec 10. PMID: 31820590.
HooKim K, Kavuri S, Lauer SR, Cohen C, Reid MD. Napsin A expression in small cell carcinoma of the lung: a cytologic study with review of differentials. J Am Soc Cytopathol. 2014 Mar-Apr;3(2):90-95. doi: 10.1016/j.jasc.2013.11.005. Epub 2013 Nov 21. PMID: 31051707.
Travis, W. Update on small cell carcinoma and its differentiation from squamous cell carcinoma and other non-small cell carcinomas. Mod Pathol 25, S18–S30 (2012). https://doi.org/10.1038/modpathol.2011.150