Background Many Americans with metastasised colon cancer do not receive indicated palliative chemotherapy. We examined the effects of health insurance and physician supplies on such chemotherapy in California.

Methods We analysed registry data for 1199 people with metastasised colon cancer diagnosed between 1996 and 2000 and followed for 1 year. We obtained data on health insurance, census tract-based socioeconomic status and county-level physician supplies. Poor neighbourhoods were oversampled and the criterion was receipt of chemotherapy. Effects were described with rate ratios (RR) and tested with logistic regression models.

Results Palliative chemotherapy was received by less than half of the participants (45%). Facilitating effects of primary care (RR=1.23) and health insurance (RR=1.14) as well as an impeding effect of specialised care (RR=0.86) were observed. Primary care physician (PCP) supply took precedence. Adjusting for poverty, PCP supply was the only significant and strong predictor of chemotherapy (OR=1.62, 95% CI 1.02 to 2.56). The threshold for this primary care advantage was realised in communities with 8.5 or more PCPs per 10 000 inhabitants. Only 10% of participants lived in such well-supplied communities.

Conclusions This study's observations of facilitating effects of primary care and health insurance on palliative chemotherapy for metastasised colon cancer clearly suggested a way to maximise Affordable Care Act (ACA) protections. Strengthening America's system of primary care will probably be the best way to ensure that the ACA's full benefits are realised. Such would go a long way towards facilitating access to palliative care.