Clinical investigation of malignant mesothelioma in Japan

The asbestos-related problems caused much social concern; however, no large-scale study was conducted about clinical features of MM in Japan. Patients with MM who have a history of occupational asbestos exposure (AE) are provided worker's compensation in Japan. However, only about 10% of MM cases were actually claimed and compensated. So there is still controversy over the association between MM and AE. The aim of this study is to investigate the clinical features of MM. We also aimed to clarify the association between MM and occupational AE in Japan.

We examined the clinical features of MM cases. Clinical information was obtained including gender, age, site of origin, pathological subtype, radiological findings, and treatment outcome. To investigate the association between MM and AE, investigators interviewed all patients regarding work and residential history.

Between January 2005 and December 2007, 105 cases (median age: 63 years, range 35-80, male/female: 88/17) were diagnosed with MM in the Rosai Hospital group and related facilities. Among them, 94(89.5%) cases originated in the pleura, 7(6.7%) in the peritoneum, 2(1.9%) in the pericardium, and 1(0.9%) in the tunica vaginalis testis. There were 69(65.7%) epithelioid, 19(18.1%) biphasic, 16(15.2%) sarcomatoid, and 1 unclassified pathological subtypes of MM. A favorable survival rate was indicated in the patient group of MPM that underwent surgery compared to others, though it was not statistically significant (P = 0.1743). The occupational AE was indicated in 89 cases (84.8%). Three patients had no history of occupational AE, but lived with someone who was in an occupation that handled asbestos. There were two patients in which AE was indicated in their life environment. Altogether, AE was indicated in 93(88.6%) patients.

This study stresses the urgent need for physicians to acknowledge the association between MM and AE, and to inquire thoroughly regarding AE to the patients with MM.