BackgroundPharmacological treatment of malignant tumors in obese patients has been reported from several perspectives. Physiological changes may affect the kinetics of anticancer drugs (e.g., lipophilicity, distribution volume, and metabolism), consequently affecting their efficacy and safety profile. However, specific guidelines for antineoplastic agent dose adjustment according to body weight, mainly due to the under-representation of obese patients in clinical trials, are currently lacking. Moreover, considering that certain tumor development is associated with obesity, the clinical management of obese patients is often complex. We herein report the antitumor treatment options of three obese patients with malignant tumors and review relevant literature to analyze the dosage of antitumor drugs in this setting. This study aims to provide additional data for the clinical treatment of obese patients with malignant tumors.Case presentationIn Case 1, carboplatin was administered at a fixed dose, mainly because of neurotoxicity risk. A maximum creatinine clearance rate (glomerular filtration rate) of 125 mL/min is recommended to prevent carboplatin overdose and toxicity. The maximum carboplatin dose was calculated using the following formula: maximum dose = area under the curve (AUC) x (125 + 25). Methotrexate dose was calculated based on the actual body weight of Cases 2 and 3. While receiving methotrexate, the blood drug concentration was within the reference range (24-h reference concentration <= 10 mu mol/L), and no serious adverse reactions occurred. As seen in the three cases, considering the particularity of some drugs, for example, more than 90% of carboplatin is excreted through the kidney, carboplatin should be administered at a fixed dose, while other chemotherapy drugs can be administered according to the actual body weight as much as possible according to the patient's condition.ConclusionsThe toxicity of chemotherapy has traditionally been assessed based on the actual body weight of obese and non-obese patients. In clinical practice, overweight and obese cancer patients often receive reduced doses of chemotherapy drugs. According to the guidelines set by the American Society of Clinical Oncology, the positive association between the use of chemotherapy and treatment-related toxicity in obese patients lacks evidence. After comprehensive consideration of complications, chemotherapy dose should be determined based on the body surface area(BSA) calculated based on actual body weight, rather than estimated or idealized body weight.