P24: The predictive role of the WHO histological classification in the treatment of advanced thymoma

Background: A recent report from the ITMIG has demonstrated that the WHO histological classification (WHO-HC) is not a prognostic factor for thymoma. We previously reported that the WHO-HC is a good predictive factor for therapeutic response in patients with advanced thymoma (Tagawa et al. Surg Today 2011;41:1599–604). The purpose of the present study is to examine the results of multimodal therapies for advanced thymoma and to reevaluate the predictive role of the WHO-HC using the updated data.

Methods: A retrospective review was performed on 54 patients with Masaoka stage III and IV thymoma who were treated from 1975 to 2014 at Kyushu University and the National Kyushu Cancer Center, Japan. The patient characteristics, treatment strategy, therapeutic response and outcomes were investigated in relation to the WHO-HC.

Results: Fifty-four patients (male, n=28; female, n=26) underwent multimodal treatments at a median age of 58 years. The Masaoka stages of the patients were as follows: stage III (n=22; 41%), IVa (n=25; 46%) and IVb (n=7; 13%). Six patients had myasthenia gravis and four patients had pure red cell aplasia. As the initial therapy, surgery (S), chemotherapy (CT), radiotherapy (RT) and chemoradiotherapy (CRT) were performed in 25, 19, 5 and 5 patients, respectively. Macroscopic complete resection was achieved in 14 of 25 patients (56%). The 5-year and 10-year overall survival rates were 72.8% and 50.1%, respectively. A univariate analysis indicated that the WHO type A–B2 (P=0.029) and surgical cases (P<0.0001) were associated with a better prognosis. Of the 32 patients who did not undergo upfront surgery, or who underwent an R2 resection, 17, 8 and 7 patients were treated with CT, RT and CRT as the first-line treatment, respectively. The CT regimen included ADOC (cisplatin, doxorubicin, vincristine, cyclophosphamide) in six patients, cisplatin plus amrubicin in five patients, carboplatin plus paclitaxel in two patients, carboplatin plus etoposide in two patients and others in nine patients. The response rate to the first-line therapy in the 19 patients with WHO type A–B2 was significantly better than that in the 13 patients with type B3, regardless of treatment modality (84.2% vs. 15.4%, P=0.0003). Only the WHO-HC (A–B2 vs. B3) was independently associated with the therapeutic response to first-line therapy (P<0.0001).

Conclusions: Type A–B2 thymoma showed a higher response rate to treatment than type B3. The WHO-HC is thus considered to be a good predictive factor for the therapeutic response in patients with advanced thymoma and should be used when determining the treatment strategy.

Keywords: Thymoma; WHO histological classification (WHO-HC); predictive factor