Determinants of Severe Oral Mucositis Development Despite Photobiomodulation Therapy in Stem Cell Transplant Patients.

: Oral mucositis (OM) is an extremely common and debilitating side effect in patients undergoing Hematopoietic Stem Cell Transplantation (HSCT). As such, managing this condition is an obligatory component for their supportive care. Among the available treatment options, photobiomodulation therapy has long since established itself as the most promising approach, with consistent evidence supporting its efficacy. Despite this, the clinical results of this therapy are still influenced by the chosen dosimetry parameters, as well as patient-specific factors. Therefore, this study aimed to assess which factors can continue to influence the severity and onset of OM despite the protective effect provided by the ongoing photobiomodulation therapy. : To achieve this, a retrospective analysis was conducted on the medical records of 171 patients who underwent PBMT during HSCT over a two-year period at the Brazilian Institute of Cancer Control. These files were used to review clinical and laboratorial parameters, such as OM grade, serum CRP, creatinine, urea, OGT, PGT, pain levels, presence of microorganisms in cultures, type of transplant, and conditioning regimens. All of these were evaluated at two different time points: the first day of conditioning and the day of highest OM degree. The statistical analysis was then conducted to evaluate the correlation between the variables and OM grade. : Results showed that type of conditioning regimens, use of MTX during conditioning, presence of microorganisms in cultures, and increased serum CRP, PGT, and initial urea levels were associated with severe OM. : Among these, the type of conditioning regimens, MTX usage, positive results in cultures, and increased PGT levels on the first day of conditioning could be considered predictive for severe OM and the worst PBMT results. Consequently, in patients exposed to additional risk factors, adjustments in dosimetry paraments of PBMT or employment of adjuvant therapies should be considered to achieve better results.