Stepwise increase of MIB-1 index in frequently relapsed malignant peritoneal mesothelioma

We identified the stepwise increase of MIB-1 index in a long-surviving malignant peritoneal mesothelioma (MPM) patient with a history of frequent relapse. A 29-year-old Japanese woman showed upper abdominal induration with adnexal tumor. Imaging study with biochemical analyses strongly suggested peritoneal tumor. On primary surgery, all tumors were resected completely without any residual tumor. Histologically, the tumor was diagnosed as MPM, for which she received adjuvant chemotherapy containing platinum agent. Two years later, the tumor relapsed in her pelvic cavity, but was resected completely with hysterectomy and salpingo-oophorectomy. Histologically, the tumor was diagnosed as MPM relapse. She underwent intraperitoneal chemotherapy with cisplatin that achieved progression-free survival of 5 years. However, relapse was detected again in pelvic cavity without any dissemination in upper abdominal cavity. The tumors were completely removed and were revealed to be compatible with MPM. She received gemcitabine and carboplatin chemotherapy. However, 2 years later, the tumor relapsed again in left upper abdominal cavity, for which she wouldn't receive 4th treatment. To investigate the longevity of this patient in association with the histologic findings, the MIB-1 index was examined in the primary and relapse tumors. The rate of MIB-1 index positive cells was calculated by counting 500 cells. MIB-1 indices were 4.2 ± 1.1 (mean ± SE), 11.8 ± 2.3, and 37.3 ± 2.5 in primary, 1st- and 2nd-relapsed tumor, respectively, demonstrating stepwise increase of MIB-1 expression over the surviving time of more than 9 years. Increase in MIB-1 index was not associated with mitotic index but may be indicating drug sensitivity, resulting in >2-year progression-free interval in each relapse.