1. Early-stage or in situ cancer: Chemotherapy may not be necessary, and it could have negative effects. 

2. Elderly patients or those with comorbidities: This group has low tolerance and is not suitable for chemotherapy. 

3. Tumors that do not require chemotherapy: Some cancers, like renal clear cell carcinoma, differentiated thyroid cancer, and gastrointestinal stromal tumors, may not respond well to chemotherapy.

4. Patients with drug resistance: If patients have already undergone multiple chemotherapy treatments and developed drug resistance, it's best to explore alternative treatment methods. 

5. Patients in the terminal stage of cancer: For those nearing the end of their lives, choosing not to undergo chemotherapy and focusing on enjoying their remaining time may be a better option.