An Australian-based nomogram predicting nodal positivity for breast cancer in older patients.

ABSTRACT

INTRODUCTION: Regional nodal status is one of the most powerful prognosticators in breast cancer. The sentinel lymph node biopsy (SLNB) evaluates the first node in the axillary lymphatic basin theorised to drain the anatomical region of breast cancer. Recent literature has appropriately raised the query of the need for SLNB for breast cancer in older patients (BCOP). Though some early-stage older patients may safely have SLNB omitted, we are potentially missing the under-represented aggressive cancers. No sentinel lymph node metastases nomogram has been developed solely from BCOP data to date. This study aimed to identify older patients with breast cancer at risk for nodal involvement using a nomogram developed from their data alone. METHODS: A retrospective analysis of prospectively collected data on BCOP (aged ≥70 years) was performed using the Breast Surgery Quality Audit (BQA). Inclusion criteria were T1-2 invasive breast cancer patients that underwent a SLNB from 1st January 2001 to 31st December 2019. The primary outcome was nodal involvement. Data obtained from the dataset included age, tumour type, tumour size in millimeters, histological grade, lymphovascular invasion, oestrogen receptor status, progesterone receptor status, HER2 status and referral source. Binary logistic regression was used to develop a nomogram. The model was internally validated by splitting the data set (80% for training and 20% for testing). A receiver operating characteristic curve was developed, with the area under the curve (AUC) and a calibration plot. RESULTS: There were 22,313 patients of which 14,856 (66.6%) were symptomatic presentations and 7457 (33.4%) were screen-detected. Invasive tumour type, tumour size, tumour grade, lymphovascular invasion, oestrogen receptors, and referral source indicated a statistically significant effect on predicting a nodal positivity event (Table 1). The AUC was 0.782 (95% CI 0.776-0.789) (Fig. 1a) and demonstrated good calibration (Fig. 1b). The negative predictive value established was 85%. CONCLUSION: We have developed an Australian sentinel lymph node metastasis nomogram for BCOP using routine histopathological data obtained pre-operatively (Fig. 2). This is the first Australian nomogram, as well as the first nomogram developed solely for BCOP - and maintains a superior AUC compared to other well-established nomograms.