Abstract IA027: DCIS or cancer? Why all the confusion?
Authors: Narod Steven A. 
Published: December 2022

Abstract
Many women diagnosed with DCIS in the United States report they are confused about their chances of developing an invasive breast cancer or metastatic cancer. They are told that DCIS is not cancer but it holds the possibility of becoming a cancer. Nevertheless, DCIS is treated in much the same way as a small invasive cancer. Surgical options include lumpectomy alone, lumpectomy with radiotherapy, unilateral or bilateral mastectomy. Much of the confusion is generated by the current paradigm that separates DCIS and invasive cancer into distinct conditions. The mortality of DCIS is 3% over 20 years and that prevention of local invasive recurrence post-DCIS does not reduce breast cancer mortality. If the invasive recurrence were the real cancer then preventing it would reduce the risk of dying but this has not been shown. Further, the risk of an invasive in-breast recurrence following DCIS is the same as the risk of an invasive in-breast recurrence following invasive breast cancer. In the Banting database, the 15-year risk of invasive local recurrence following DCIS was 15.6%, following stage I breast cancer was 15.3% and following stage II breast cancer was 15.9%. In the Banting database, the 15-year risk of ipsilateral invasive recurrence was 14% for DCIS patients who receives radiotherapy and was 29% for DCIS patients who did not received radiotherapy – a difference of 15%. In the Banting database, the 15-year risk of ipsilateral invasive recurrence was 14% for Stage I/II patients who received radiotherapy and was 27% for Stage I/II patients who did not receive radiotherapy – a difference of 13%. The benefit of radiotherapy is the same in both groups. Similarly, the benefit of unilateral mastectomy versus lumpectomy on preventing local invasive recurrence is the same for DCIS patients as it is for early-stage invasive breast cancer patients. In our SEER-based analysis of 812,851 women with breast cancer, the 25-year actuarial risk of contralateral invasive breast cancer was 10.1% for patients with DCIS and was 9.9% for patients with invasive breast cancer. Based on this finding, the benefit of performing a contralateral mastectomy at the time of diagnosis is the same for both groups. We accept lumpectomy as standard of care for invasive breast cancer even though the risk of invasive ipsilateral recurrence is much higher after lumpectomy than after mastectomy. We consider contralateral mastectomy as an option for women with invasive cancer, but as overtreatment for women with DCIS even though the risk of contralateral breast cancer is almost exactly the same. The benefit of radiotherapy is the same for patients with DCIS and stage I/II breast cancer, but we are more likely to consider it overtreatment for DCIS patients. Much of the confusion can be resolved if we consider both types of cancer to be different points on the spectrum. Breast cancer is heterogeneous; DCIS is one end of the spectrum. Accepting this fact will make the rationale behind treatment decisions easier to explain.
Citation Format: Steven A. Narod. DCIS or cancer? Why all the confusion? [abstract]. In: Proceedings of the AACR Special Conference on Rethinking DCIS: An Opportunity for Prevention?; 2022 Sep 8-11; Philadelphia, PA. Philadelphia (PA): AACR; Can Prev Res 2022;15(12 Suppl_1): Abstract nr IA027.