Evaluating total tumor load (TTL) to predict metastasis in four or more axillary lymph nodes in HR +/HER2- breast cancer patients: the TULIP4N + study

PURPOSE: To validate the predictive value of Total Tumor Load (TTL), based on Cytokeratin 19 (CK19) mRNA copy number measured by OSNA in sentinel lymph nodes (SLNs), and to establish an optimal cut-off for identifying HR + /HER2- breast cancer (BC) patients at high risk of ≥ 4 metastatic lymph nodes (LNs), eligible for adjuvant abemaciclib therapy. PATIENTS/METHODS: A retrospective, international, multicenter study pooling data from six studies conducted between 2000 and 2016 in adult BC patients with SLN biopsies analyzed by OSNA. Variables were TTL (CK19 mRNA copies/µL) in SLNs, number of LNs removed, and number of metastatic ones. We constructed receiver operating characteristics (ROC) curves to determine optimal TTL values and multivariate logistic regression models to identify relevant prognostic factors for predicting ≥ 4 LN metastases. RESULTS: We included 3804 patients with HR + /HER2- tumors of any histological type, complete axillary LN dissection, and > 4 LNs removed; 608 (16.0%) had ≥ 4 metastatic LNs and 439 had lobular BC. At cut-offs of 99,500 and 101,000 copies/µL, TTL had a 32.3% and 32.4% PPV. In lobular BC, cut-offs between 92,305 and 108,700 copies/µL reached a 40% PPV. In lobular HR + /HER2- BC, a multivariate model including tumor grade, TTL, and lymphovascular invasion reached a 49% PPV for predicting ≥ 4 metastatic LNs, yielding a nomogram and an online calculator for use in routine practice. CONCLUSION: TTL measured using OSNA predicts ≥ 4 metastatic LNs in patients with luminal-like BC, with a proposed optimal threshold of 100,000 copies/µL. TRIAL REGISTRATION: Not applicable.