TAC Chemotherapy Cycle Interval
The TAC (docetaxel/doxorubicin/cyclophosphamide) regimen is administered every 21 days (3 weeks) for 6 cycles with mandatory filgrastim support. 1
Standard Dosing Schedule
The NCCN guidelines establish the following TAC protocol: 1
- Docetaxel 75 mg/m² IV on day 1
- Doxorubicin 50 mg/m² IV on day 1
- Cyclophosphamide 500 mg/m² IV on day 1
- Cycle repeats every 21 days for 6 cycles
- All cycles require filgrastim (G-CSF) support 1
Clinical Context and Evidence Base
TAC is listed as a preferred adjuvant regimen by NCCN for HER2-negative breast cancer, though it has been somewhat superseded by dose-dense AC followed by taxane regimens in more recent guidelines. 1, 2
The landmark BCIRG-001 trial (TAX316) established TAC's efficacy with 10-year follow-up data showing: 3
- Disease-free survival of 62% versus 55% for FAC (HR 0.80, p=0.0043)
- Overall survival of 76% versus 69% for FAC (HR 0.74, p=0.0020)
- Consistent benefit across nodal, hormone receptor, and HER2 subgroups
Critical Safety Considerations
The every-3-week schedule with mandatory G-CSF support is non-negotiable due to significant hematologic toxicity. 1
Key toxicity monitoring includes: 3
- Grade 3-4 neutropenia occurs in the majority of patients despite G-CSF support
- Grade 3-4 heart failure occurred in 3% of patients in the pivotal trial
- Substantial LVEF decrease (≥20% from baseline) occurred in 17% of patients
- Six cases of leukemia/myelodysplasia were reported in the TAC arm
Cardiac monitoring is mandatory given anthracycline exposure, with baseline and periodic LVEF assessments required throughout treatment. 3
Comparison to Alternative Regimens
While TAC uses a 21-day cycle, other contemporary regimens employ different schedules: 1, 2
- Dose-dense AC followed by paclitaxel uses 14-day cycles (every 2 weeks)
- TC (docetaxel/cyclophosphamide without anthracycline) uses 21-day cycles for only 4 cycles
- Sequential AC→T regimens typically use 21-day cycles for AC, then either weekly or every-3-week paclitaxel
The 21-day TAC schedule represents a balance between efficacy and tolerability, though dose-dense strategies with 14-day intervals have shown superior outcomes in some populations when G-CSF support is provided. 2