Understanding Chemotherapy Cycles
What is a Chemotherapy Cycle?
A chemotherapy cycle consists of a treatment period (when drugs are given) followed by a rest period (to allow the body to recover), typically repeated at regular intervals—most commonly every 21 days (3 weeks) or 28 days (4 weeks). 1
Standard Cycle Lengths by Cancer Type
Breast Cancer
- 21-day cycles are most common: drugs given on day 1, then repeated every 3 weeks 1
- 28-day cycles for certain regimens: drugs given on specific days (e.g., days 1,8,15), then 2-week rest 1
- 14-day dose-dense cycles: accelerated schedule requiring growth factor support 1
Lung Cancer (NSCLC)
- 21-day cycles are standard for platinum-based doublets 1
- Duration: 2-4 cycles for stage III disease with concurrent radiation 1
- Duration: 4-6 cycles maximum for stage IV disease 1
Ovarian Cancer
- 21-day cycles for 6 cycles with paclitaxel/carboplatin 1
- 28-day cycles for dose-dense weekly paclitaxel regimens 1
Testicular/Germ Cell Cancer
- 21-22 day cycles for BEP (bleomycin, etoposide, cisplatin) 1, 2
- 3 cycles for good prognosis, 4 cycles for intermediate/poor prognosis 1
Why the Rest Period Matters
The rest period between treatments allows:
- Bone marrow recovery: white blood cells, platelets, and red blood cells regenerate 1, 3
- Normal tissue repair: healthy cells recover from chemotherapy damage 4
- Toxicity management: side effects resolve before next treatment 1
Critical timing rule: Postpone treatment maximum 3 days only if fever present, neutrophils <500/mL, or platelets <100,000/mL 1
Total Number of Cycles
Evidence-Based Limits
- Breast cancer adjuvant: 4-6 cycles standard 1, 5
- Lung cancer stage III: 2-4 cycles with radiation (no more than 4 cycles) 1
- Lung cancer stage IV: 4-6 cycles maximum (no benefit beyond 6 cycles) 1
- Ovarian cancer: 6-8 cycles for advanced disease 1
- Testicular cancer: 3-4 cycles depending on risk group 1
Key principle: Extending chemotherapy beyond these limits increases toxicity without survival benefit 1, 6
Dose Intensity Considerations
Maintain planned dose intensity by avoiding delays and dose reductions whenever possible 1:
- Use growth factors (G-CSF) prophylactically if prior infectious complications occurred 1, 3
- For adjuvant breast cancer, cumulative cisplatin dose ≥300 mg/m² improves outcomes 1
- Maximum treatment time should not exceed 7 weeks for concurrent chemoradiation 1
Common Pitfalls to Avoid
- Do not extend first-line chemotherapy beyond 4-6 cycles in advanced disease—no survival benefit, only increased toxicity 1, 6
- Do not delay chemotherapy until performance status worsens—start while patient has good functional status 1
- Do not reduce doses for neutropenia alone—use growth factor support instead to maintain dose intensity 1
- Do not use aluminum-containing needles or IV sets with cisplatin—causes precipitation and loss of potency 2
Practical Example: AC-T Regimen for Breast Cancer
This illustrates how cycles work in practice 1, 5:
Phase 1 (AC):
- Doxorubicin 60 mg/m² + Cyclophosphamide 600 mg/m² IV on day 1
- Cycle repeats every 21 days for 4 cycles (12 weeks total)
Phase 2 (T):
- Paclitaxel 80 mg/m² IV weekly for 12 weeks
- Or Paclitaxel 175 mg/m² every 21 days for 4 cycles
Total treatment duration: approximately 24 weeks 1