not very
Chemotherapy is debilitating and expensive. It can cause heart failure and irreversible damage to nerves and the lining of the gut. 20% of cancer related deaths following cancer therapy may be hastened or caused by the toxic effects of the chemotherapy itself and not by the cancer:-
Mortality within 30 days of receiving systemic anti-cancer therapy at a regional oncology unit: what have we learned?
‘378 patients who received cytotoxic chemotherapy and targeted therapy. In total 13 deaths (3.4%) occurred within 30 days following SACT. Three deaths (23%) were definitely treatment-related - neutropenic sepsis, pneumocystis pneumonia and bowel perforation.’
To put up with this risk and toxicity how effective is it?
Only a small minority drugs approved by the FDA and EMA show evidence that improvements in surrogate markers, such as tumour shrinkage, are correlated with improvements in survival:-
https://georgiedonny.substack.com/p/how-effective-is-chemotherapy