The association between lymph node status and the tumor size in breast cancer - results from the Danish Breast Cancer Group (DBCG).

Background and purpose: The association between the tumor size and the risk of lymph node metastasis (LNM) is well known. The purpose of this study is to describe a new model for predicting the occurrence of LNM at an earlier time for breast cancer patients where at a given time this association is known. Patient/material and methods: The subjects studied were 59,400 breast cancer patients treated in the period 1995-2012 and registered in the Danish Breast Cancer Group (DBCG) database. Data included age, year of treatment, menopausal status, tumor size, lymph node status, localization, focality, histological type, grade, estrogen receptor (ER), HER2 status, lympho-vascular invasion (LVI), and type of surgery. Univariate and multivariate analyses were made.

Results: 46% of patients presented with LNM. The occurrence increased with increasing tumor size. HER2 positive tumors had more LNM 56.9% versus 44.7% (p < 0.001) (odds ratio [OR] 1.17 [95% confidence interval, CI 1.09-1.26]) and mostly pronounced in relation to ER negative tumors (p < 0.001). ER negative/HER2 negative tumors had lower risk of LNM (OR 0.57 [95% CI 0.52-0.63]). Central tumors and tumors in the lower lateral quadrant were more often node positive. LVI showed increased odds for LNM (OR 5.16 [95% CI 4.84-5.52]).

Interpretation: Increasing tumor size is the only time-dependent risk of LNM. HER2 positive tumors had an increased risk of LNM, and ER negative/HER2 negative tumors had a decreased risk of LNM. LVI was associated with substantial increased risk of LNM. The knowledge of breast cancer patient and tumor characteristics at a given time may predict stage of cancer at an earlier time.