Objectives Most cytostatics used in cancer treatment are dosed on body surface area (BSA). To administer an appropriate dose it is therefore necessary to know the patient’s correct body weight. However, evidence is lacking on how often, after initiation of treatment, body weight should be measured to recalculate BSA. We aimed to assess the relevance of weight measurements during chemotherapy treatment.

Methods Over a 2 year period we analysed BSA changes in adult patients undergoing chemotherapy treatment. The frequency of and median time to ≥10% BSA change was determined. We assumed a 10% BSA change required dose adjustment and was therefore clinically relevant.

Results Using a database query, data from 2276 patients were used for descriptive statistics, life table analyses and generalised estimating equations. The frequency of ≥10% BSA change occurred in a maximum of 7.6% of the patients, depending on the tumour type. Descriptive statistics in the indications with more than 100 patients showed that BSA changes of ≥10% occurred after 84 days. The groups with the earliest BSA changes were patients with acute leukaemia, lymphoma and pancreatic cancer.

Conclusions Our observations from real-world data indicate it is safe to omit the current requirement for monthly weight measurements. We advise that during chemotherapy, measuring the body weight in patients who have acute leukaemia, lymphoma or pancreatic cancer or who are under 20 years of age, should be performed at least every 3 months. For other patients, extending this period to a 6-monthly weight measurement should be considered.