PORT Improves Relapse-Free Survival in Thymic Carcinoma, Not Thymoma

Postoperative radiotherapy does not improve overall survival in stage II or III thymic carcinoma or thymoma, but thymic carcinoma patients may benefit in terms of relapse-free survival

medwireNews: Postoperative radiotherapy (PORT) prolongs relapse-free survival (RFS) in patients with stage II or III thymic carcinoma, but not in those with stage II or III thymoma, according to a Japanese study published in Cancer.

However, none of these patient populations experienced any overall survival (OS) benefits following PORT, report Hiroshi Date, from Kyoto University, and colleagues, who analysed records for 1265 patients in the Japanese Association for Research on the Thymus (JART) database.

The 5-year RFS rate for individuals with Masaoka stage II thymic carcinoma who underwent PORT (n=25) compared with those who did not (n=27) was 91.3% and 68.1%, respectively. But these results did not reach statistical significance, which the authors attribute to the low number of cases.

In stage III thymic carcinoma patients, PORT (n=51) resulted in a 5-year RFS rate of 50.5% versus 26.1% for the no-PORT (n=44) group, a difference that was statistically significant.

The combined hazard ratio (HR) for RFS, after adjusting for stage and residual tumour after resection, was 0.48, which led Hiroshi Date et al to conclude that PORT accords an RFS benefit for stage II and III thymic carcinoma patients.

For stage II thymoma patients, the 5-year RFS rate did not differ significantly between the PORT (n=196) and no-PORT (n=615) groups, at 93.4% versus 92.3%. Nor did it differ significantly in stage III thymoma patients, with comparable rates of 62.0% and 69.3% for those who did (n=119) and did not (n=143) receive PORT, respectively.

The 5-year OS rate was similar between the PORT and no-PORT groups for stage II and stage III thymic carcinoma patients, at 91.1% versus 86.8% and 65.0% versus 64.0%, respectively.

PORT-treated stage II thymoma patients had a 5-year OS rate of 96.5%, which was comparable with a rate of 96.2% for their counterparts who did not receive PORT. And for stage III patients, the rates for PORT and no-PORT were 92.9% and 89.7%, respectively.

The researchers conclude that PORT has a positive impact on stage II and III thymic carcinomas, but add that their findings “support the declining trends of PORT for stage II and III thymoma in Japan.”

However, in an accompanying editorial, Andreas Rimner, from Memorial Sloan Kettering Cancer Center in New York, USA, urges that the thymoma findings be interpreted with caution as “the absence of an improvement in RFS or OS in an imbalanced retrospective data set with a significant potential for referral bias should not be interpreted as the absence of a positive effect of PORT.”

He concludes: “Ultimately, prospective studies are needed to determine the role of PORT in thymic malignancies.”

References

Omasa M, Date H, Sozu T, et al. Postoperative radiotherapy is effective for thymic carcinoma but not for thymoma in stage II and III thymic epithelial tumors: The Japanese Association for Research on the Thymus Database Study. Cancer 2015; Article first published online 6 January. doi:10.1002/cncr.29166

Rimner A. Postoperative radiotherapy: Not all thymic malignancies are created equal. Cancer 2015; Article first published online 6 January. doi:10.1002/cncr.29164

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