Cancer risk in individuals with polydactyly: a Swedish population-based cohort study

Background Polydactyly is a feature of several cancer predisposition syndromes (CPS), however, cancer risk in individuals with polydactyly is largely unknown.

Methods We performed a matched cohort study using data from Swedish national registers.

We included 6694 individuals with polydactyly, born in Sweden between 1970–2017.

Polydactyly was categorised as thumb polydactyly, finger polydactyly, polydactyly+ (additional birth defects and/or intellectual disability) or isolated polydactyly.

Each exposed individual was matched to 50 comparisons by sex, birth year and birth county.

Associations were estimated through Cox proportional hazard models.

Findings An increased childhood cancer risk was found in males (HR 4.24, 95% CI 2.03–8.84) and females (HR 3.32, 95% CI 1.44–7.63) with polydactyly+.

Isolated polydactyly was associated with cancer in childhood (HR 1.87, 95% CI 1.05–3.33) and young adulthood (HR 2.30, 95% CI 1.17–4.50) in males but not in females.

The increased cancer risk remained after exclusion of two known CPS: Down syndrome and neurofibromatosis.

The highest site-specific cancer risk was observed for kidney cancer and leukaemia.

Conclusions An increased cancer risk was found in individuals with polydactyly, especially in males and in individuals with polydactyly+.

We encourage future research about polydactyly and cancer associations and emphasise the importance of clinical phenotyping.