Comparative analysis of cell morphology in sputum samples homogenized with dithiothreitol, N-acetyl-L cysteine, Cytorich(®) red preservative and in cellblock preparations to enhance the sensitivity of sputum cytology for the diagnosis of lung cancer.

Background: Lung cancer claims highest rate of cancer related mortality worldwide, mainly due to late diagnosis and distant metastasis. Sputum cytology is the simplest, non-invasive and cost effective technique but it has low sensitivity due to lack of robust processing methods to retrieve all the diagnostic materials clogged in mucus, inflammatory exudates and blood.

Methods: This study have compared conventional pick and smear method of sputum processing with samples prepared by homogenization methods using N-acetyl-l-cysteine, Dithiothreitol (DTT), CytoRich red solution and cell blocks (CBs) with respect to screening time, quality of staining, cellularity, smear background, nuclear and cytoplasmic morphology preservation, and diagnostic efficacy. The significance of CB prepared from homogenised samples for immunocytochemistry, protein extraction, Genomic DNA and RNA extraction were also evaluated on a cohort 3,185 samples. The significance of the morphological features in each of the techniques was statistically analysed using SPSS 11 software.

Results: The smear background clarity, staining quality and diagnostic efficacy of samples processed in red solution was found to be superior to the conventional method (P < 0.0001), where as samples homogenized in DTT showed a better cellularity (P < 0.0001). CBs prepared from samples homogenized in red solution were found to be very significant (P < 0.0001) in increasing the diagnostic efficacy compared to other two methods. Immunocytochemistry and DNA extraction were found possible in CBs as well as from the cell suspension. A combined analysis of smears and CBs found to improve the sensitivity of sputum cytology.

Conclusion: The study suggests homogenization of sputum in CytoRich ® red solution and cellblock preparations routinely for all samples to improve the sensitivity of sputum cytology. IHC and DNA extraction can be performed in sputum samples suggesting the role of sputum samples for ancillary techniques.