Thymic Tumor Surgical Resection Margins Less Than 1mm Show Decreased Recurrence Rate Independent of Radiation Therapy (RT)
Rola H Ali, Caroline Mariano, Winson Y Cheung, Nevin Murray, Diana N Ionescu. BC Cancer Agency, Vancouver, BC, Canada
Background: The best approach in the management of thymoma and thymic carcinoma is unclear. Patients referred to the British Columbia Cancer Agency (BCCA) with stage I disease are treated primarily with surgery while selected stage II patients receive adjuvant RT.
Design: This study presents a specific cohort of patients with stage II thymic epithelial neoplasms identified from a larger population-based cohort of cases referred to the BCCA from 1994 to 2009. Potential tumor-related prognostic factors (TRPF) including WHO subtype, tumor size, capsular presence and integrity, degree of invasion, distance to the closest margin and lymphoid hyperplasia were assessed by 2 pathologists following the 2011 published policies adopted by the International Thymic Malignancy Interest Group. Clinical data including age, sex, stage, treatment, recurrence and survival data were available for statistical analysis and correlation. Kaplan-Meier methodology was used to evaluate the relationship between margin status and overall survival (OS) and progression free survival (PFS).
Results: From a cohort of 170 patients, 54 stage II patients with known margin status were selected. Of these, 39 cases were Masaoka stage IIa and 15 were stage IIb. There were 28 females and 26 males, with a mean age of 64 years. There were 50 thymomas (5 type A, 9 type AB, 8 type B1, 18 type B2, 6 type B3, 3 mixed, 1 other) and 4 thymic carcinomas. 18 patients had surgery alone, 33 surgery and RT, 2 tri-modality treatment, and 1 no treatment. A total of 35 patients received RT. Of the surgically treated cases, 22 tumors had pathologically positive margins and 32 negative but close margins (20 at <0.5mm; 10 at 0.5-1mm; 2 at >1mm margin). Of the 22 patients with positive margins, 17 received RT and of those 4 recurred. Of the 30 patients with negative margins less than 1mm, 16 received RT and none recurred. Of the 14 patients with negative margins who were not irradiated, none recurred. Based on Kaplan-Meier curves, there were no statistically significant differences between margin status and OS (p=0.72), but there was a trend towards worse PFS in those with a positive margin (p=0.06).
Conclusions: Positive surgical margin status does not always trigger RT but may represent a negative prognostic factor for PFS in some stage II thymic epithelial malignancies. Patients with surgical resection margins within less than 1mm (but negative) show a decreased recurrence rate independent of RT and significantly better PFS than those with positive margins.
Wednesday, March 21, 2012 9:30 AM
Poster Session V # 288, Wednesday Morning