PURPOSE:Unintentional weight loss (UWL) is a prevalent problem in people with cancer and is associated with poorer psychosocial outcomes. A gap exists in understanding whether and how perceived and/or weight status impacts experiences of UWL. Thus, we sought to examine subjective experiences of UWL in people with cancer, and whether perceived and/or actual weight status impacts these experiences. METHODS:Participants were recruited through Cancer Support Community's Cancer Experience Registry® and related networks. Participants completed an online survey that included the FAACT Anorexia-Cachexia subscale, and 19 items that captured six themes related to "beliefs and concerns" (positive beliefs, psychosocial impact, physical impact, cancer outcomes, self-esteem, relationships with others). Perceived weight status (PWS) was assessed using a single item. Body mass index (BMI) was calculated using self-reported weight and height measurements. RESULTS:Of 326 respondents, 114 reported experiencing UWL. Over one-third misperceived their weight, with 29% perceiving weight status as below their BMI status. UWL in those with perceived weight status of overweight/obese was associated with positive beliefs. However, being underweight by BMI or perceiving oneself as underweight were both associated with greater concerns about weight loss. Perceived weight status of underweight compared to normal or overweight/obese weight status was associated with poorer psychosocial well-being, personal control, self-esteem, and relationships with others. CONCLUSION:In people with cancer, perceived weight status, rather than BMI, had greater impact on negative "beliefs and concerns" about UWL. Findings suggest assessment of both perceived and actual BMI to address the impact of UWL on psychosocial wellbeing.