E55: Optimizing Treatment Decisions in Microinvasive Ductal Carcinoma in Situ: Evaluating the Need for Surgical Axillary Staging

Surgical axillary staging is debated in clinically Microinvasive Ductal Carcinoma in Situ (cT1mi) due to the low occurrence of nodal metastasis. This study aims to assess the utility of axillary staging in clinically node-negative (cN0) T1mi breast cancer and provide insight for optimizing surgical treatment.

Methods:

This retrospective cohort study analyzed data from the National Cancer Database to investigate axillary status of patients with cT1mi breast cancer from 2012-2019. Patient demographics, clinical characteristics, treatment methods and pathologic findings were collected. Comparisons were made between those who did and did not undergo axillary surgery (ASx) and of those who did, between patients who were pathologically node-positive (pN+) vs. pathologic node-negative (pN-).

Results:

Of 10,843 patients analyzed, 9,220 (85.0%) underwent ASx, 1,623 (15.0%) did not. Mean age undergoing ASx and those who did not was 59.2±11.2 and 66.3±12.8 years, respectively. On univariate analysis, factors associated with ASx were private insurance, fewer medical comorbidities, HER2+ or triple negative, higher grade, lymphovascular invasion and mastectomy. Sentinel node biopsy was performed in 83%. Axillary lymph node dissection (ALND) in 17%. Final pathology upgrade to true invasive cancer (T1 or greater) happened in 29.3% of cases. Of 9,069 who underwent ASx with known pathologic nodal status, 8,512 (93.9%) were pN- and 557 (6.1%) were pN+. Factors associated with odds of positive nodes were younger age, Black race, lymphovascular invasion, and mastectomy. Of pN+ patients, 64 (0.7%) had ≥3 positive nodes and would require ALND. On subset analysis of the 4,190 patients undergoing mastectomy, 244 (5.8%) did not undergo ASx, while 3,946 (94.2%) did, of whom 373 (9%) were pN+. Regarding adjuvant treatment, more patients who underwent ASx received chemotherapy (12% v. 8%) Those who were pN+ were more likely to receive chemotherapy (58% v. 12%). Similar proportions of patients who did and did not undergo Asx received adjuvant radiation (5% v. 4%). Those undergoing Asx, a higher proportion of pN+ underwent radiation (32% v. 5%). 

Conclusions:

Surgical axillary staging for patients with cT1mi breast cancer is common, despite majority being pathologically node-negative. A higher proportion are being subjected to morbidity of ASx than supported by pathologic stage. Nodal status impacts decision for adjuvant therapy. Identifying patient factors associated with upgrade and higher probability of pN+ may allow personalized surgical options to minimize ASx morbidity.