Between 1998 and 2016, 140,293 female patients in the SEER database underwent mastectomy-coded NSM (5765, 4.1%) and TM (134,528, 95.9%). We visually assessed the changes in four basic surgical methods from 1998 to 2016. The proportion of NSM increased steadily, while that of TM began to decline after 2013 (Fig. 1). Most of the patients treated with NSM were 46–65 years old (3213, 35.3%) and married (3857, 66.9%). Most of the patients treated with NSM were White (4472, 77.6%), and a small number (506, 8.8%) were Black. The overall median household income of patients receiving treatment ranged from $50,000 to $70,000 (Table 1).
In patients undergoing NSM, grade I–II was reported in the majority of patients (3611, 62.6%). Overall, T1 (3348, 58.1%) and N0 (3948, 68.5%) were the most abundant stages. Surgical laterality was left in 50.2% (2892/5764) of patients. A total of 81.2% of patients were ER positive, 72.1% of patients were PR positive, and 16.1% of patients were HER2 positive. Among the available molecular subtype data, HR+/HER2- (3649, 63.3%) was the most common. The same trend was observed in patients undergoing TM (Table 1).
Radiation and Chemotherapy
A total of 17.2% of patients underwent adjuvant radiation therapy. Among the patients who underwent NSM, 22.3% received adjuvant radiotherapy and 77.7% had a nonradiation/unknown status. Among the patients who underwent TM, 17.0% received adjuvant radiotherapy, and 83.0% had a nonradiation/unknown status. In contrast, more patients received chemotherapy. A total of 43.4% of the patients underwent adjuvant chemotherapy. Among the patients who underwent NSM or TM, 49.9% and 43.2%, respectively, received adjuvant radiotherapy (Table 1).
After PSM matching, 5763 patients receiving NSM and 17,289 patients receiving TM were included in the analysis (Table 1). It was noted that the 5-year (94.61% vs 93.00%) and 10-year (86.34% vs 83.48%) OS rates of the NSM group were higher than those of the TM group and that the 5-year (96.16% vs 95.74%) and 10-year (92.20% vs 91.37%) BCSS rates of the NSM group were higher than those of the TM group (Fig. 2). Kaplan-Meier survival curves and log-rank test indicated that the OS and BCSS were similar between the NSM group and the TM group (P = 0.058 and 0.87, respectively).
Survival analysis showed that age, marital status, race, median household income, tumor grade, N stage, ER status, PR status, molecular subtype, radiation, and chemotherapy were significant factors for the OS and BCSS of patients treated with NSM. At the same time, year of diagnosis and HER2 status were significant factors for OS, and histology was a significant factor for the BCSS (P < 0.05) (Supplementary Fig. 1 A–N). For OS, patients with age > 65, single marital status, Black race, low-median household income (< $50,000), diagnosed from 1998 to 2003, tumor grade III–IV, N3 stage, ER negative, PR negative, HER2 enriched, triple negative breast cancer (TNBC) subtype, radiotherapy and chemotherapy had worse prognosis. For BCSS, patients with Black race, tumor grade III–IV, N3, lobular carcinoma, ER negative, PR negative, TNBC, radiotherapy and chemotherapy had a worse prognosis.
For OS, the forest plot showed that there was a significant difference when comparing the efficacy of NSM and TM. Some of the variables showed that NSM was beneficial for breast cancer patients compared with TM (Fig. 3), including age > 46, White race, median household income ≥ $70,000, ER positive,PR positive, HER2 negative, HR+/HER2- subtype, nonradiotherapy, and nonchemotherapy (P < 0.05). For BCSS, none of the subgroups showed significant differences (Fig. 4). This means that NSM was non-inferior to TM. These results may indicate that NSM has similar prognostic value compared with TM in breast cancer patients and shows greater advantages in some subgroups.