Malignant Pleural effusion due to small cell carcinoma of lung, with a 3x2x2 cm lung mass
Cytopathology:
- 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.
Reference:
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