Patient demographics and baseline characteristics

During the study period, data for 471,299 patients diagnosed with breast cancer were extracted. Of these, 78,777 were eligible for the primary analyses, with 41,733 (53.0%) in the luminal-type group and 37,044 (47.0%) in the triple-negative group (Fig. 2).

The proportions of patients with unknown data, including missing data, were 25.0% in T factor, 5.8% in N factor, 6.3% in M factor, and 26.7% in the clinical stage groups (data not shown). Of the 37,044 patients in the triple-negative group, 27,278 (73.6%) patients had no pre- or postoperative therapy records, implying insufficient follow-up in this population (Online Resource 4).

The post hoc analyses using a revised study population generated using new eligibility criteria evaluated a total population of 42,636 surgical patients diagnosed with breast cancer. Of these, 32,133 patients (75.4%) were in the luminal-type group, and 10,503 (24.6%) were in the triple-negative group (Fig. 2). All the following results are from the post hoc analyses.

Table 1 summarizes the baseline characteristics of patients from the post hoc analysis population. In the overall luminal-type group (n = 32,133), patients had a median (min–max) age of 63 (19–100) years, and 26,679 (83.0%) and 5454 (17.0%) patients had clinical stage II and III breast cancer, respectively (Online Resource 5).

Table 1 Patient characteristics by new exclusion criteria

In the luminal-type group, 13,526 (98.7%) patients received perioperative therapy, of whom 12,773 (94.4%) were treated with regimens including anthracyclines and/or taxane, in addition to endocrine therapy. In the triple-negative group, 5987 (57.0%) patients received perioperative chemotherapy, and of those, 5594 (93.4%) were treated with regimens including anthracyclines and/or taxane.

Patients who received chemotherapy, including anthracycline, taxane, or both, tended to be younger at a median (min–max) age of 54 (19–87) years than those who did not receive chemotherapy. Patients who underwent concurrent and sequential anthracycline + taxane regimens had median (min–max) ages of 53 (31–81) years and 53 (21–86) years, respectively. Patients undergoing only endocrine therapy had a median (min–max) age of 69 (23–100) years. Among patients undergoing chemotherapy including regimens with anthracycline, taxane, or both, anthracycline + taxane concurrent and sequential regimens, 44 (27.2%) and 2342 (31.5%) patients had clinical stage III disease, respectively. Among patients not receiving regimens with anthracycline or taxane 165 (21.9%) had clinical stage III disease.

In the overall triple-negative group (n = 10,503), the median (min–max) age of patients was 65 (23–100) years; 8363 (79.6%) had clinical stage II disease, while 2140 (20.4%) had clinical stage III disease (Table 1). Among patients receiving chemotherapy containing anthracycline, taxane, or both, anthracycline + taxane concurrent and sequential chemotherapy regimens had median (min–max) ages of 56 (32–85) and 57 (23–85) years, respectively (Online Resource 6). Among patients receiving concurrent (n = 70) or sequential (n = 3691) chemotherapy regimens with both anthracycline and taxane, 26 (37.1%) and 892 (24.2%) had clinical stage III disease, respectively (Online Resource 6).

Selection of preoperative and/or postoperative therapy

In the luminal-type group (n = 32,133), postoperative therapy alone was the most common treatment (24,590 patients [76.5%]). This was followed by 6917 patients (21.5%) who received both pre- and postoperative therapies and 219 patients (0.7%) who received only preoperative therapy (Fig. 3a). A total of 18,200 patients (56.6%) received endocrine therapy alone. Among the patients who received only preoperative therapy (n = 219), 121 (55.3%) patients were treated with endocrine therapy alone, and among those who received only postoperative therapy (n = 24,590), 16,150 (65.7%) patients were treated with endocrine therapy alone. In both pre- and postoperative therapy (n = 6917) chemotherapy regimens, anthracycline, taxane, or both tended to be more likely to be received as preoperative therapy than other regimens (preoperative in preoperative + postoperative: 4186 patients [60.5%]) (Fig. 3b).

Fig. 3

Treatment pattern in perioperative anti-tumor therapy. a Proportion of patients for each perioperative therapy. b Proportion of patients with regimens during the perioperative period. c Proportion of patients with regimens including anthracycline, taxane, or both during the perioperative period. A anthracycline, T taxane

Among chemotherapy regimens including anthracycline, taxane, or both, anthracycline + taxane sequential regimens tended to be used as preoperative or postoperative therapy (preoperative only: 79/97 patients [81.4%], postoperative only: 3887/7895 patients [49.2%], and preoperative in preoperative + postoperative: 3216/4186 patients [76.8%]). When a regimen containing anthracycline, taxane, or both was selected as postoperative therapy in patients with both pre- and postoperative therapies (n = 6917), taxane only or anthracycline + taxane sequential regimens were more likely to be received as treatment (postoperative in preoperative + postoperative: taxane only, 434/906 patients [47.9%] and anthracycline + taxane sequential, 313/906 patients [34.5%]) (Fig. 3c).

In the triple-negative group (n = 10,503), 4516 patients (43.0%) had no record of either pre- or postoperative therapy (Fig. 3a). In total, 3327/10,503 patients (31.7%) received only postoperative therapy, followed by 1683/10,503 patients (16.0%) receiving only preoperative therapy, and 977/10,503 patients (9.3%) received both pre- and postoperative therapies. Regarding treatment patterns, chemotherapy regimens including anthracycline, taxane, or both were administered in about 90% or more of cases where pre- or postoperative therapy was received (preoperative only: 1667/1683 patients [99.0%], postoperative only: 2982/3327 patients [89.6%], and preoperative in preoperative + postoperative: 930/977 patients [95.2%]), whereas a regimen not containing anthracycline, taxane, or both was selected as postoperative therapy: 658/977 (67.3%) in triple-negative patients (Fig. 3b). When both pre- and postoperative therapies were received (n = 977), chemotherapy regimens without anthracycline or taxane were received as postoperative therapy in 658/977 patients (67.3%). Among patients receiving chemotherapy with anthracycline, taxane, or both, anthracycline + taxane sequential regimens were more likely to be selected as pre- or postoperative therapies than other regimens containing anthracycline, taxane, or both (preoperative only: 1369/1667 patients [82.1%]; postoperative only: 1766/2982 patients [59.2%]; and preoperative in preoperative + postoperative: 635/930 patients [68.3%]) (Fig. 3c). When regimens containing anthracycline, taxane, or both were used as postoperative therapy in patients with both pre- and postoperative therapies (319/977 [32.7%]), a regimen containing taxane only was received by a higher proportion of patients (224/319 [70.2%]).

Factors contributing to the prescription of regimens, including anthracycline, taxane, or both

Table 2 summarizes the ORs for receiving regimens containing anthracycline, taxane, or both. In the luminal-type group, patients ≥ 40 years of age were less likely to receive chemotherapy regimens including anthracycline, taxane, or both than patients < 40 years of age (number of patients, [%], OR [95% CI]  < 40 years, 968/1381 patients [70.1%]; 40–49 years, 3733/6383, [58.5%], 0.62 [0.54–0.70]; 50–59 years, 3195/5624, [56.8%], 0.56 [0.49–0.63]; 60–69 years, 3417/7605, [44.9%], 0.33 [0.29–0.38]; and ≥ 70 years, 1460/10733, [13.6%], 0.06 [0.05–0.06]).

Table 2 Odds ratios for patients receiving regimens containing anthracycline and/or taxane in pre- or postoperative therapy

Patients treated at facilities that were not cancer treatment centers (2044/6278 patients [32.6%]) tended to receive regimens containing anthracycline, taxane, or both less often than those in specialized cancer treatment centers (10,729/25,448 patients [42.2%]) (OR [95% CI] 0.65 [0.60–0.70]). Patients with clinical stage II (9467/26,341 patients [35.9%]) tended to be prescribed regimens containing anthracycline, taxane, or both less often than those with clinical stage III (3306/5385 patients [61.4%]) (OR [95% CI] 0.24 [0.22–0.25]).

In the triple-negative group, patients aged 60–69 years (1644/1718 [95.7%]) and ≥ 70 years (1062/1345 [79.0%]) tended to be prescribed regimens containing anthracycline, taxane, or both less often than those aged < 40 years (453/459 [98.7%]) (OR [95% CI] 0.30 [0.13–0.69] and 0.05 [0.02–0.12], respectively). In addition, patients treated at hospitals with capacities of < 200 beds (111/132 patients [84.1%]) less often received regimens including anthracycline, taxane, or both, compared with those treated at hospitals with capacities of 200–499 (2833/3052 patients [92.8%]) and ≥ 500 beds (2650/2803 patients [94.5%]) (ORs [95% CI] 1.77 [1.02–3.09] and 2.00 [1.10–3.64], respectively). Additionally, regimens containing anthracycline, taxane, or both were less likely to be administered in facilities that were not cancer treatment centers (918/1016 patients [90.4%]) than in those specializing in cancer treatment (4676/4971 patients [94.1%]) (OR [95% CI] 0.74 [0.55–0.99]).

Treatment duration for each treatment regimen

For regimens with anthracycline only and taxane only in the luminal-type group, the most common treatment duration was 6– < 10 weeks (anthracycline only, 592/1235 patients [47.9%]; taxane only, 2171/3279 patients [66.2%]). The most common duration for concurrent anthracycline + taxane treatment was 10– < 14 weeks (42/87 patients [48.3%]). For anthracycline + taxane sequential regimens, the most common treatment duration was 18– < 24 weeks (2679/4200 patients [63.8%]). In regimens not including anthracycline or taxane, 226/1275 patients (17.7%) had treatment durations of 2– < 6 weeks and 204/1275 patients (16.0%) had treatment duration of 6– < 10 weeks. When only endocrine therapy was received, 6636/21,431 patients (31.0%) and 7177/21,431 patients (33.5%) had treatment durations of 18– < 24 weeks and 24–28 weeks, respectively (Fig. 4a).

Fig. 4

Proportion of patients in each category of treatment duration. Treatment duration was stratified into 0– < 2, 2– < 6, 6– < 10, 10– < 14, 14– < 18, 18– < 24, and 24–28 weeks from the first prescription date of initial adjuvant therapy to the date of death, the date of loss to follow-up of treatment regimen duration, the date of censoring at 30 September 2021, or the date of the prescription after 24 weeks, whichever occurred first. a Luminal-type, and b triple-negative group. A anthracycline, T taxane

For chemotherapy regimens with anthracycline only and taxane only in the triple-negative group, the most common treatment duration was 6– < 10 weeks (anthracycline only, 256/612 [41.8%] patients; taxane only, 425/861 patients [49.4%]). The most common treatment duration for the anthracycline + taxane concurrent regimen was 10– < 14 weeks (14/37 patients [37.8%]). For the anthracycline + taxane sequential regimen, 18– < 24 weeks treatment durations were the most common (1009/1791 patients [56.3%]). In regimens not including anthracycline or taxane, 253/1003 patients (25.2%) had treatment durations of 18– < 24 weeks, 187/1003 (18.6%) had treatment durations of 2– < 6 weeks, and 162/1003 (16.2%) had treatment durations of 6– < 10 weeks (Fig. 4b).