DCIS-MI is a special type of breast cancer, and there is little evidence on the prognosis of patients with DCIS-MI undergoing BCS + RT and mastectomy. We found that the prognosis of patients with DCIS-MI after mastectomy is not better than those of BCS + RT in any subgroup by using the SEER database.
In the NCCN guidelines, DCIS-MI is classified as early-stage invasive breast cancer. All surgical options for early-stage invasive breast cancer are unified. There is no special explanation for the surgical options for DCIS-MI. In our study, 71.9% of patients with DCIS-MI were older than 50 years. Besides, patients with DCIS-MI had few lymph node metastases (92.3% without lymph nodal metastases), low histological grade (61.3% in GI + II), and high positive rates of ER and PR (72.3% and 59.3%), which was consistent with other studies [21, 22]. These results indicate that DCIS-MI has a good prognosis.
Although the clinicopathological features of DCIS-MI all indicate a good prognosis, at present, there are still a large number of DCIS-MI patients undergoing mastectomy. In our study, 47.83% of the patients received mastectomy. In Eastern countries, the proportion of patients with DCIS-MI undergoing mastectomy is higher, even as high as 80% [23, 24]. At present, the safety of mastectomy for DCIS-MI has been verified. Mamtani et al.studied the locoregional and distant recurrence after mastectomy for DCIS with or without microinvasion. It proved that locoregional recurrence after mastectomy for DCIS ± microinvasion is uncommon. Even in the age group with the highest recurrence rate, 10-year locoregional recurrence remains low at 4.2%. DCIS-MI often has multiple minimally invasive foci, associated with a higher risk of ipsilateral recurrence [26, 27]. The study of Si et al. showed that 35.1% of DCIS-MI Patients have multiple foci, which had a worse disease-free survival rate compared with one-focus patients (98.29 vs. 93.01%, P = 0.032). The safety of BCS for DCIS-MI is worth exploring. Rakovitch compared the local recurrence rate after breast-conserving in patients with DCIS and DCIS-MI . The results showed that multiple foci of MI are associated with an increased risk of invasive local recurrence in women with DCIS treated with BCS, but treatment with the whole breast and boost RT can mitigate this risk. The Yale School of Medicine retrospective clinical study of BCS included 72 patients with DCIS-MI and 321 patients with DCIS, all of whom received local radiotherapy. There was no difference in regional recurrence rates after 10 years between the DCIS-MI group and the DCIS group (8.3% vs. 6.8%) . These studies proved that BCS + RT is safe for DCIS-MI.
Studies have confirmed the safety of BCS + RT in DCIS patients. Park et al. conducted a study on 3648 patients with DCIS younger than 40 years old, and the results showed that mastectomy does not offer survival benefits over BCS + RT . Mamtani et al. also confirmed this . To our knowledge, only Bartova et al. compare the prognostic difference between BCS and mastectomy in DCIS-MI. They followed up 41 patients with DCIS or DCIS-MI after BCS and mastectomy, and finally, only 27 patients completed the follow-up. There is no local recurrence occurred . However, the sample size of this study was small, and no survival rate was reported. Our study showed that the BCS + RT group showed significantly higher OS and BCSS than patients in the mastectomy group. In order to find out which subgroups of people can benefit from BCS + RT, we also conducted a subgroup analysis and found that the OS and BCSS outcomes of mastectomy were not better than those of BCS + RT in any subgroup. Furthermore, we observed that 95.5% of patients received mastectomy without RT in our study. Thus we think that BCS + RT showed a better prognosis than mastectomy may due to RT. Studies have confirmed that RT can reduce the local recurrence of breast cancer. Rakovitch et al. proved that postoperative radiotherapy could reduce the local recurrence rate in patients with DCIS-MI . The EORTC study also demonstrated that adjuvant radiotherapy after BCS could reduce the risk of ipsilateral invasive recurrence by approximately 50% during 10 years of follow-up .
Similar to the result of aother study, chemotherapy cannot improve the survival of DCIS-MI. Pu et al. proved that postoperative chemotherapy did not improve DFS in patients with DCIS-MI after mastectomy (HR = 1.50, 95%CI 0.29–7.87, P = 0.63). Chen et al. analyzed 3198 DCIS-MI patients and concluded that chemotherapy was an independent factor for worse BCSS (P = 0.008) and there was no statistical significance for OS (P = 0.248) in patients with DCIS-MI .In our study’s overall cohort, 6.2% and 14.8% of patients in the BCS + RT group and the mastectomy group received chemotherapy, respectively. There was no significant difference in OS and BCSS between those who did not receive chemotherapy and those who received chemotherapy (all P > 0.05) after PSM. However, further studies are needed to verify whether chemotherapy is beneficial to patients with DCIS-MI.
Our study had several limitations. Firstly, there may be residual confounders even though the propensity-matched landmark analysis was used. Secondly, the SEER database did not provide detailed information on breast multiple lesions and lacks data on postoperative breast reconstruction and postoperative local recurrence. Finally, there is no information on endocrine therapy and targeted therapy in the SEER database.