Neighbourhood migrant density is increasingly recognised as a social determinant of health. However, its association with hospitalised patients with cancer outcomes, such as mortality and readmission rates, remains understudied. This study examined whether neighbourhood migrant density influenced these outcomes and whether these associations varied before and during the COVID-19 pandemic.

Retrospective cohort study.

Swedish national registers.

Hospitalised patients with cancer (ICD code C00–C97) from 2014 to 2019 (before the pandemic) and 2020–2021 (during the pandemic).

90-day mortality and readmission rates. Independent variables were neighbourhood migrant density—categorised as total, Western and non-Western migrants (as a proportion of the total area population).

We identified 243 357 hospitalised patients with cancer before the pandemic and 112 935 during the pandemic. Swedish-born individuals and Western migrants residing in high migrant density neighbourhoods had higher rates of 90-day mortality (incidence rate ratio, IRR: 1.15, 95% CI 95% CI 1.12 to 1.19 and IRR: 1.09, 95% CI 1.00 to 1.18) and readmission (IRR: 1.16, 95% CI 1.13 to 1.19 and IRR: 1.14, 95% CI 1.07 to 1.22). During the pandemic, 90-day mortality rates significantly increased among Western migrants and 90-day readmission rates increased for all patients from high migrant density neighbourhoods.

High neighbourhoods migrant density was associated with increased 90-day mortality and readmission among Swedish-born individuals and Western migrants before the pandemic. These outcomes were exacerbated during the pandemic, particularly among migrants. Cancer care for residents in neighbourhoods with high migrant density needs to be improved, especially during public health crises.