Breast Cancer Treatment (PDQ®): Treatment - Health Professional Information [NCI] - Stage I, II, IIIA, and Operable IIIC Breast Cancer
Table 6. Standard Adjuvant Chemotherapy Regimens for Stage I, II, IIIA, and Operable IIICHER2/neuNon-Overexpressing Breast Cancer continued...
Cognitive impairment has been reported to occur after the administration of some chemotherapy regimens. However, data on this topic from prospective randomized studies are lacking.
The EBCTCG meta-analysis revealed that women who received adjuvant combination chemotherapy did have a 20% (standard deviation = 10) reduction in the annual odds of developing contralateral breast cancer. This small proportional reduction translated into an absolute benefit that was only marginally statistically significant, but it indicates that chemotherapy does not increase the risk of contralateral disease. In addition, the analysis showed no statistically significant increase in deaths attributed to other cancers or to vascular causes among all women randomly assigned to receive chemotherapy. The use of anthracycline-containing regimens, however—particularly those containing an increased dose of cyclophosphamide—has been associated with a cumulative risk of developing acute leukemia of 0.2% to 1.7% at 5 years.[239,240] This risk increases to more than 4% in patients receiving high cumulative doses of both epirubicin (>720 mg/m2) and cyclophosphamide (>6,300 mg/m2).
Chemotherapy and tamoxifen risks
Adjuvant combinations of tamoxifen and chemotherapy administered concurrently to enhance efficacy may also have enhanced toxic effects. A single study randomly assigned postmenopausal women with node-positive, ER-positive tumors to receive tamoxifen (30 mg/day for 2 years) plus CMF (intravenously for 6 months) (n = 353) or tamoxifen alone (n = 352). Of the women receiving combined chemohormonal therapy, 13.6% developed one or more thromboembolic events compared with 2.6% in the tamoxifen-alone group (P < .001). Also, statistically significantly more women were on combined treatment who developed severe thromboembolic events (grade 3–5), most of which (39 of 54) occurred while the women were actually receiving chemotherapy. Not all studies that compared concurrent chemotherapy plus tamoxifen with tamoxifen alone, however, have reported such high rates. In the NSABP-B-16 study that compared tamoxifen (20 mg/day for 5 years) plus chemotherapy with doxorubicin plus cyclophosphamide (four cycles) with tamoxifen alone, 4.9% of the women on combined treatment had thromboembolic events versus 2.1% of women on tamoxifen alone. Whether tamoxifen should be given concurrently or after the completion of chemotherapy was addressed in an Intergroup trial (INT-0100 [NCT00929591], formerly SWOG-8814,) that compared the concurrent and sequential administration of CAF and tamoxifen in postmenopausal hormone receptor-positive patients. Sequential administration resulted in superior DFS that was significant at 8 years (67% vs. 62%; P = .045).[Level of evidence: 1iiDii]
Candidates for whom adjuvant therapy may not be necessary include individuals with small primary tumors (<1 cm) and negative axillary nodes who have an excellent prognosis, with nearly 90% of patients alive and free of disease at 20 years in one series. A U.S. Intergroup study (SWOG-8897) observed patients off treatment with tumors of low-risk (tumors too small for biochemical ER/PR assay) and uncertain-risk (tumors <2 cm, ER-positive and PR-positive, and low S-phase fractions). This low-risk and uncertain-risk subset had a 96% 5-year survival rate without adjuvant therapy. Whether this group of patients would derive long-term benefit from tamoxifen for either its adjuvant or preventive effects remains uncertain. Clearly, this group has a risk of developing a new breast cancer that would meet the eligibility criteria that were used in the Breast Cancer Prevention Trial that demonstrated a benefit with tamoxifen.