There are individual differences in the frequency of chemotherapy-induced nausea and vomiting (CINV) in cancer patients. We investigated the individual variability in susceptibility to CINV with focus on both behavioral factors and genetic factors in Japanese cancer patients. We performed a prospective study to investigate the association between patient attributes (backgrounds and habits as well as gene polymorphisms) and anorexia, nausea, or vomiting in 55 Japanese cancer patients undergoing chemotherapy at Nagoya University Hospital. We found that gender (female), use of non-steroidal anti-inflammatory drugs, susceptibility to motion sickness, and anxiety were associated with the frequency of CINV. Gene polymorphisms of rs1076560 (dopamine D 2 receptor gene), rs6766410 (serotonin 5-HT 3C receptor gene) and rs4680 (catechol-Omethyltransferase gene) were also associated. Our data suggest that these attributes may thus be risk factors for CINV. Our results provide novel information that can be used to predict the incidence of CINV in Japanese patients undergoing chemotherapy; this can help provide a substantial improvement in supportive care for patients with different types of cancer.Key words chemotherapy; anorexia; nausea; vomiting; gene polymorphism; risk factor Chemotherapy-induced nausea and vomiting (CINV) is one of the most distressing side effects of chemotherapy. Inadequately controlled emesis impairs functional activity and QOL for patients, increases the use of health care resources, and may occasionally compromise adherence to treatment.1,2) According to the American Society of Clinical Oncology Clinical Practice Guidelines regarding antiemetic agents in oncology, a three-drug combination of a serotonin 5-hydroxytryptamine type 3 (5-HT 3 ) receptor antagonist, dexamethasone, and aprepitant is recommended before chemotherapy treatments that have high emetic risks. If this is insufficient, substituting a high-dose of intravenous metoclopramide for the serotonin 5-HT 3 receptor antagonist or adding a dopamine D 2 receptor antagonist to the regimen is considered. 3,4) In recent years, a new class of antiemetic therapies represented by neurokinin-1 (NK-1) receptor antagonists has been introduced into clinical practice. An NK-1 receptor antagonist, aprepitant, combined with dexamethasone and the serotonin 5-HT 3 receptor antagonist ondansetron, have been shown to ameliorate CINV in both high and moderate emetic risk chemotherapy patients. 4,5) In spite of antiemetic therapy being administered according to the guidelines for CINV treatment, an incidence rate of 25-38% for delayed emesis and 55-60% for delayed nausea has been observed.4) The mechanisms underlying interpatient variability in response to treatment are not clear but are believed to be due, in part, to genetic factors. To that end, some polymorphisms in the serotonin 5-HT 3 receptor genes were investigated for their relationship with CINV. [6][7][8] There is also the possibility that polymorphisms of genes that play functional molecular or phys...