Design: Nationwide three-generation family cohort
Population: Swedish men under 69 with family cancer data across three generations
Primary outcome: Familial standardised incidence ratio for prostate cancer
Effect: Two brothers SIR 4.1; plus an uncle or grandfather 10.1

A Swedish three-generation family cancer study (BJU International, 1 October 2026) calculated familial relative risks of prostate cancer for men under 69 according to which relatives were affected.

Two affected brothers gave a standardised incidence ratio of 4.1, rising to 10.1 when an uncle or grandfather was also affected. An affected father gave 3.1, rising to 4.7 with an affected second-degree relative and up to 11.5 with more. An affected grandfather alone gave about 1.6 on either side; a maternal uncle 1.8 and a paternal uncle 1.5. The highest risk, 27, was in men with affected brothers, father and two second-degree relatives.

For young men, affected uncles and grandfathers were more common than affected fathers or brothers, so asking only about first-degree relatives misses much of the family signal. Maternal and paternal lines were equally informative - which matters because prostate cancer on the mother's side is easily overlooked.

Ask about prostate cancer in uncles and grandfathers on both sides, not just father and brothers
Record the maternal line - it carried as much risk information as the paternal
Consider earlier screening discussions for men with several affected relatives
Consider referral for genetic assessment where multiple relatives are affected

Why it matters

Family histories that stop at father and brothers miss most of the familial signal in younger men.

The statistics, in plain English

A standardised incidence ratio of 4 means four times the expected number of cancers in men of the same age. Some familial excess may reflect shared screening behaviour in families rather than inherited risk alone.