The case of a 66-year-old female patient with late diagnosis of giant anal canal mucinous adenocarcinoma invading the gluteal and vulvar regions is reported. Because of the patient's severe clinical status and disease morbidity, surgical resection of the lesion was accomplished, with no adjuvant chemo- or radiotherapy. In the postoperative period, the patient received hyperbaric oxygen therapy, which facilitated and even accelerated local healing. Total closure of the raw flesh area was achieved, with no recurrence signals of cancer being detected after one-year follow-up. We are convinced that, in this difficult case, hyperbaric oxygen therapy played a crucial role in patient recovery and wound healing, allowing for early closure with good progression.