Response assessment in metronomic chemotherapy: RECIST or PERCIST?

Introduction: Metronomic chemotherapy (MC) is a novel therapeutic variation for resistant cancers, wherein chemotherapeutic drugs are administrated in low doses with no prolonged drug-free break. It lessens the level of toxicity, is better tolerated and enhances the quality of life. This retrospective analysis was undertaken to evaluate whether anatomical (computed tomography [CT]) or functional (positron emission tomography [PET]) imaging be used for response assessment in patients on MC. Materials and Methods: A total of 16 males and 27 females with age range of 12-83 years on MC who underwent PET/CT were assessed by new response evaluation criteria in solid tumors (RECIST 1.1) and PET response criteria in solid tumors (PERCIST 1.0). Results: Concordance between RECIST 1.1 and PERCIST was seen in 32 (75%) patients. There was discordance in 11 (25%) patients. In patients with discordance, the results were confirmed by follow-up imaging. PET upstaged the disease in 81% of patients (9/11) and down-staged the disease in 19% of patients (2/11). Conclusions: Metabolic response accurately identified the disease status as assessed by clinical or imaging follow-up. Alteration in morphology takes time to manifest, which is demonstrated by CT or magnetic resonance; whereas in MC which brings about tumor dormancy, assessing metabolic response by PET would be more appropriate. MC is usually given in palliative setting but in few cases complete metabolic response was demonstrated in our study. In such a scenario this form of treatment has the potential to become an adjunct mode of treatment in some tumors. This needs to be evaluated with larger, homogenous patient population in a prospective mode.