Comparative Effectiveness of Sentinel Lymph Node Biopsy for Ductal Carcinoma In Situ

Patients with ductal carcinoma in situ (DCIS) treated with available therapies have experienced excellent outcomes and very low mortality rates due to the disease's non-invasive nature. However, considerable debate exists as to how the DCIS lesion should be treated. As a result, determining strategies to manage DCIS has been identified as a research priority. The role of sentinel lymph node biopsy (SLNB) for DCIS management is controversial in general and needs further scrutiny. Our study addresses this evidence gap as the investigators propose a retrospective cohort study to investigate the outcome of SLNB among DCIS patients. Specifically, the investigators will compare the outcomes, including survival outcomes and treatment side effects, among women older than 67 years of age with DCIS receiving SLNB vs. not receiving SLNB within 6 months of DCIS diagnosis. The investigators have two primary aims in this study: Aim 1: the investigators select our study sample using SEER-Medicare database. The investigators will determine associations between SLNB and acute/subacute side effects, including lymphedema, pain, and limitation of movement of upper extremity from the first breast conserving surgery to 9 months post-diagnosis. Aim 2: the investigators will determine associations between SLNB and long-term outcomes, including breast cancer specific mortality, ipsilateral invasive breast cancer diagnosis, subsequent mastectomy as treated recurrence, and lasting side effects, from >9 months post-diagnosis to death or the end of this study period. Given the nature of our observational study design, the investigators will apply standard multivariate analyses and propensity score methodology to reduce the influence from confounders. The investigators will control for patient demographics, comorbidities, functional status, tumor characteristics, and prior healthcare utilization. Using distance to the nearest provider that uses SLNB for DCIS or surgeon's tendency in using SLNB for stage I/II breast cancer, the investigators also plan to conduct instrument variable analyses if necessary. Stratifying patients by key DCIS characteristics (including grade, comedonecrosis, and tumor size) and their predicted life expectancy (given their age and comorbidities), the investigators also hope to identify patient subgroups who may safely forgo SLNB. The study would provide evidence on the efficacy and safety outcome of SLNB for DCIS management.