Cytology Smears: An Enhanced Alternative Method for Colorectal Cancer pN Stage—A Multicentre Study

SIMPLE SUMMARY: Recurrence of stage II (pT3-T4 pN0) colorectal cancer (CRC) occurs in about 15% of patients and it is often due to undetected lymph node (LN) metastases with conventional pathology haematoxylin and eosin (H&E) LN analysis. Despite more sensitive molecular methods of LN staging having proved to have prognostic value in stage II CRC, we aimed at determining whether the pN stage could be better assessed with LN cytology smears. We analysed 3936 LNs from 217 CRC surgical resections, using three methods, H&E, cytology smears, and the One Step Nucleic Acid Amplification (OSNA) molecular assay. We compared the pN stages obtained from both H&E and cytology, as well as with the OSNA results. We concluded that LN analysis with cytology smears not only enables performing the pN stage, but detects more LN metastases than H&E, with a similar detection rate to molecular methods. Cytology LN analysis would allow a better patient therapeutic management. ABSTRACT: Stage II colorectal cancer (CRC) recurrence remains a clinical problem. Some of these patients are true stage III CRC with a pN0 pathology stage. This large prospective multicentre cohort study aimed at evaluating the diagnostic ability of lymph node (LN) cytology smears to perform the pN stage and compare it with the conventional haematoxylin and eosin (H&E) pathology pN stage. Additionally, we used the One-Step Nucleic Acid Amplification (OSNA), a high-sensitive molecular method of LN staging. A total of 3936 fresh LNs from 217 CRC surgical specimens were examined by three methods, H&E, LN cytology smears, and OSNA. H&E detected 29% of patients with positive LNs, cytology smears 35%, and OSNA 33.2% (p < 0.0001). H&E and cytology concordantly classified 92.2% of tumours, and 88.5% between OSNA and H&E. Cytology had 96.8% sensitivity and 90.3% specificity to discriminate positive/negative patients compared to H&E (p = 0.004), and 87.3% sensitivity and 89% specificity when compared to OSNA (p = 0.56). Patients with positive LNs detected by any of the three methods had significantly worse disease-free and overall survival. We conclude that pN stage accuracy for detecting positive LNs is superior with LN cytological smears than with conventional H&E, which would enable a better pN stage and management of early-stage CRC patients.