Performance and Prognostic Relevance of Lymph Node Assessment by One-Step Nucleic Acid Amplification Assay in Rectal Cancer: A Multicenter Study.

BACKGROUND/OBJECTIVES: Lymph node metastases (LNM) undetected by standard hematoxylin and eosin (H&E) have been associated with unfavorable prognosis in colorectal cancer. The One-Step Nucleic Acid Amplification (OSNA) assay has demonstrated superior sensitivity in detecting LNM compared to H&E. We aimed to assess the performance of OSNA in detecting LNM, as well as its prognostic value in rectal cancer (RC) patients.

METHODS

Lymph nodes (LNs) of patients from 15 centers were analyzed by both H&E and OSNA. The total tumor load (TTL) was defined as the sum of cytokeratin 19 mRNA copies/µL in all LNs from a surgical specimen, using a threshold of 250 copies/μL for OSNA positivity. Cox proportional hazard regression was used to assess the effect of TTL ≥ 250 or 6000 copies/μL on cancer-specific survival (CSS) and recurrence-free survival (RFS), with Firth's method applied to account for low event rate.

RESULTS

A total of 97 RC patients were included. Of these, 84 patients were eligible for survival analysis. The sensitivity and specificity of OSNA, compared to H&E, were 91.7% and 84.7%, respectively. TTL ≥ 6000 versus <6000 copies/μL was related to worse CSS and RFS. When dividing TTL into three groups: ≤250, 250-6000, and >6000 copies/μL, only TTL ≥ 6000 copies/μL was significantly associated with worse CSS and RFS.

CONCLUSIONS

The OSNA assay is highly sensitive for detecting LNM in RC patients. A TTL of ≥6000 copies/μL could identify a subset of RC patients with worse CSS and RFS who might benefit from adjuvant treatment or intensive surveillance.