Abstract 325P
Background
Axillary level I-II node (ALN) status is used to stratify breast cancer risk and inform systemic therapy decisions. We sought to investigate the association of breast tumour location with ALN involvement, use of chemotherapy, and breast cancer-specific survival (BCSS).
Methods
Patients diagnosed with stage T1-2 M0 breast cancer from 2004 to 2019 were identified from the SEER 17 registries database. Tumour locations were classified as outer quadrant, inner quadrant, or central. Covariates were age, race, median household income, year of diagnosis, tumour size, histology, grade, and ER/PR/HER2 status. Propensity score weighting with Bayesian additive regression trees was used to balance covariates between tumour locations. Doubly robust estimation was then performed with multivariable logistic and Cox regressions to assess the association of tumour location with binary outcomes and BCSS, respectively.
Results
A total of 453,387 patients with a median follow-up of 70 months were eligible for analysis, of whom 293,070 (65%) had outer quadrant tumours, 127,237 (28%) had inner quadrant tumours, and 33,560 (7%) had central tumours. After propensity score weighting, the rates of ALN metastases for outer quadrant, inner quadrant, and central tumours were 28.2%, 20.2%, and 32.6%, respectively. Chemotherapy was given to 38.0%, 36.5%, and 38.8% of patients. Ten-year BCSS were 91.6%, 91.0%, and 90.5%. Compared to outer quadrant tumours, inner quadrant tumours had lower odds of ALN metastases (OR 0.62; 95% CI 0.61-0.63; P<0.001) and central tumours had higher odds (OR 1.30; 95% CI 1.26-1.33; P<0.001). Similarly, inner quadrant tumours had lower odds of receiving chemotherapy (OR 0.90; 95% CI 0.88-0.91; P<0.001) while central tumours had higher odds (OR 1.07; 95% CI 1.04-1.10; P<0.001). BCSS was worse in both inner quadrant (HR 1.07; 95% CI 1.04-1.10; P<0.001) and central (HR 1.10; 95% CI 1.04-1.15; P<0.001) tumours.
Conclusions
The risk of ALN metastases from breast cancer varies with tumour location. Inner quadrant tumours have worse BCSS than outer quadrant tumours despite a lower risk of ALN metastases. Reliance on ALN staging without consideration of tumour location may lead to treatment decisions that are inconsistent with breast cancer risk.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
The authors.
Funding
Has not received any funding.
Disclosure
All authors have declared no conflicts of interest.
Resources from the same session
323P - Macrophage population analysis of the breast cancer microenvironment within the context of seroma formation after mastectomy (SerMa pilot study)
Presenter: Felicitas Schneider
Session: Poster session 02
326P - Sentinel lymph node mapping in breast cancer: Evaluating the dual-tracer method with indocyanine green and radioisotope
Presenter: Ava Kwong
Session: Poster session 02
328P - Frequency of radiotherapy-induced malignancies in Li-Fraumeni syndrome patients with early breast cancer and influence of the radiotherapy technique
Presenter: Vanessa Petry
Session: Poster session 02
329P - Pulmonary function and lung fibrosis up to 12 years after breast cancer radiotherapy
Presenter: Jarle Karlsen
Session: Poster session 02
330P - Effect of radiotherapy in deep inspiration in patients with left breast cancer: Does the size of the target area affect the dose for the most crucial organs at risk?
Presenter: Zoltan Locsei
Session: Poster session 02
331P - miR-21 and miR-34a as biomarkers of radiotherapy skin adverse events in ductal carcinoma in situ
Presenter: Tanja Marinko
Session: Poster session 02
332P - Early prediction of residual cancer burden to neoadjuvant chemotherapy in breast cancer by longitudinal MRI-based multitask learning: A multicenter cohort study
Presenter: Wei Li
Session: Poster session 02
333P - Evaluation of a composite PET/CT and HER2 tissue-based biomarker to predict response to neoadjuvant HER2-directed therapy in early breast cancer (TBCRC026)
Presenter: Maeve Hennessy
Session: Poster session 02