BACKGROUND

The one-step nucleic acid amplification (OSNA) assay is a novel molecular method that can detect metastasis in a whole lymph node based on cytokeratin 19 mRNA copy number. This cohort study aimed to establish an OSNA-based nodal staging (pN(mol)) classification for breast cancer.

METHODS

The cohort consisted of 1039 breast cancer patients who underwent sentinel node (SN) biopsy using the OSNA assay. Cutoff value of the SN tumour burden stratifying distant disease-free survival (DDFS) was determined, and predictive factors for DDFS and breast cancer-specific survival (BCSS) were investigated. pN(mol) classification of the SN status was defined as: pN0(mol)(sn), SN negative; pN1mi(mol)(sn), SN positive and tumour burden <cutoff-value; and pN1(mol)(sn), tumour burden ⩾cutoff-value. Median follow-up time; 68.3 months.

RESULTS

Cutoff value of the SN tumour burden was 2810 copies per μl. Of the 1039 patients, 798, 95, and 146 had pN0(mol)(sn), pN1mi(mol)(sn), and pN1(mol)(sn) status, respectively. Five-year DDFS and BCSS rates were lower for pN1(mol)(sn) patients than for pN1mi(mol)(sn) patients (87.7% vs 98.8%, P=0.001 and 93.1% vs 98.8%, P=0.044, respectively). Multivariate analyses revealed the pN(mol) classification was most significant predictor for DDFS and BCSS.

CONCLUSIONS

The molecular-based pN classification determines the prognosis of breast cancer patients and could guide therapeutic decision making.