DIFFERENTIATED THYROID-CANCER - IMPACT OF ADJUVANT EXTERNAL RADIOTHERAPY IN PATIENTS WITH PERITHYROIDAL TUMOR INFILTRATION (STAGE PT4)

BACKGROUND. The role of adjuvant external radiotherapy in the survival of patients with differentiated thyroid cancer (DTC) is controversial . To our knowledge, no attempt has been undertaken thus far to assess the impact of this therapy with respect to the papillary and follicula r types of thproid cancer as separate entities. METHODS. Between 1979 and 1999, 238 patients with differentiated papillary thyroid cancer (P TC) and follicular thyroid cancer (FTC) with Stage pT4 have been treat ed and followed in our clinic. One hundred sixty-nine patients free of metastases at the final staging, which was performed after the second radioiodine therapy, were included in this study. The standard treatm ent comprised total thyroidectomy, ablative radioiodine therapy, and t hyroid-stimulating hormone-suppressive therapy with levothyroxin. Nine ty-nine patients free of disease after the final staging received addi tional external radiotherapy to the neck (with a dose of 50-60 Gy), wh ereas the remaining 70 patients were treated with the standard treatme nt protocol only. Distributions of age, sex, and follow-up time were c omparable in both irradiated and nonirradiated groups. Multivariate an alysis of the influence of age, sex, histologic subtype, and lymph nod e status as well as of external radiotherapy on the time to first loco regional and distant failure (LDF), and the time to locoregional recur rence (LR), was accomplished using Cox's proportional hazard model. RE SULTS. In patients with DTC, external radiotherapy was a predictive fa ctor for improvement of both LR (P = 0.004) and locoregional and dista nt failure (P = 0.0003). When the time to first locoregional and dista nt failure was calculated separately for patients with PTC and FTC, th ere was a significant difference in the PTC group in favor of irradiat ed patients (P = 0.0001), whereas there was no effect of external radi otherapy in the FTC group (P = 0.38). Further analyses disclosed that this effect was significantly present only in patients with PTC and ly mph node involvement (P = 0.002), whereas those without lymph node inv olvement did not benefit from an additional adjuvant radiotherapy (P = 0.27). Because none of the patients younger than age 40 years died du e to the disease nor had progressive disease during follow-up, we reas sessed our results in patients older than age 40 years. The effect of external radiotherapy could be confirmed in this subgroup of patients (P = 0.0009) and in the subgroup of lymph node positive patients older than age 40 years with invasive PTC (P = 0.01). CONCLUSIONS. In addit ion to total thyroidectomy, treatment with radioiodine, and TSH-suppre ssive therapy with thyroid hormone, adjuvant external radiotherapy imp roves the recurrence-free survival in patients older than age 40 years with invasive PTC and lymph node involvement. (C) 1996 American Cance r Society.