Background: Hand-foot syndrome (HFS) is a side effect of sunitinib with considerable impact on quality of life. Seasonal variation and hyperhydrosis are possibly correlated to occurrence of HFS. Therefore, we proposed to study the prevalence of HFS in different seasons retrospectively and to study the relationship between sunitinib sweat secretion and HFS prospectively. Patients and methods: A retrospective cohort of 19 patients treated with sunitinib was used to determine seasonal prevalence of HFS. In a prospective study, sunitinib and N-desethyl sunitinib levels in sweat patches of 25 patients treated with sunitinib were quantified and correlated to severity of HFS. Results: In the retrospective cohort, the patients suffered from more severe HFS during summertime compared with the rest of the year. In the prospective study, the cumulative amounts of sunitinib plus metabolite measured in the patches of the ontreatment phase (median 129.4 ng/patch) were higher than the off-treatment phase (median 39.5 ng/patch). A tendency was observed towards increasing amounts of drug per patch with increasing severity of HFS. Conclusion: Patients experienced more HFS in summer time compared to other seasons. However, no statistically significant correlation between sunitinib sweat secretion and severity of HFS could be demonstrated within our patient cohort.