Some With Locally Advanced Thyroid Cancer Benefit From Adjuvant Radiation
By Marilynn Larkin
NEW YORK (Reuters Health) – Adding external beam radiation therapy (EBRT) to radioactive iodine (RAI) leads to good disease control in locally advanced, differentiated thyroid cancer, especially for patients with tracheal or esophageal invasion who received aggressive surgical resection, researchers say
“The vast majority of patients with differentiated thyroid cancer have rather indolent tumors and excellent prognosis with surgery alone,” Dr. Mark Zafereo of the University of Texas MD Anderson Cancer Center in Houston told Reuters Health.
“However, a small minority - about 5% - of differentiated thyroid cancer patients have more aggressive tumor biology and a more aggressive clinical disease course, with higher rates of cancer recurrence and poorer rates of survival relative to their cancer,” he said by email.
“These patients require not only surgery, but also other therapies such as RAI, and even EBRT in select cases,” he noted. “However, the decision for adjuvant therapy after surgery is complex and must take into account patient quality of life, side effects of treatment, and the ultimate prognosis of the patient with regard to the full spectrum of their disease throughout their body.”
To investigate, Dr. Zafereo and colleagues reviewed data on 88 patients (mean age, 58; half women) who had been treated surgically for T4a-differentiated thyroid cancer at their center from 2000 through 2015.
Half the patients had adjuvant RAI alone and half had RAI plus EBRT, according to the JAMA Otolaryngology-Head and Neck Surgery report, online November 2.
Those who underwent RAI alone did not receive EBRT because of invasion into the recurrent laryngeal nerve only (32%) or into the tracheal perichondrium and/or esophageal muscularis only (41%).
Disease-free survival at five years was 52%, with rates of 43% in patients receiving RAI alone and 57% in those receiving RAI and EBRT.
The RAI-alone group had five-year overall survival and disease-specific survival rates of 76% and 89%, respectively; corresponding rates for the RAI+EBRT group were and 79% and 86%. Differences between the groups were not significant.
Patients undergoing RAI alone had a higher rate of locoregional failure (82%), compared with those who underwent RAI+EBRT (18%).
Independent predictors of worse disease-free survival were age (adjusted hazard ratio, 1.02/year) and esophageal invasion (aHR, 2.30).
“(Since) an exploratory analysis demonstrated that locoregional failure was more likely in patients with minimal involvement of the tracheal perichondrium or esophageal muscularis, further studies investigating the role of EBRT in these patients is warranted,” Dr. Zafereo said.
“Due to the potential adverse effects of EBRT, improved precision of the indications for it is required to balance the benefits and risks of treating patients with locally advanced thyroid cancer,” he affirmed.
Future studies may determine whether targeted drug therapies – e.g., tyrosine kinase inhibitors - may allow clinicians to scale back immediate postoperative adjuvant therapy, especially postoperative adjuvant EBRT, for patients with locally advanced, invasive disease, he added. “Instead of immediate postoperative radiation, some of these patients may be able to be treated with targeted drug therapy further down the line should their disease recur locally.”
Surgical oncologist Dr. Christopher Fundakowski of Temple University and Fox Chase Cancer Center in Philadelphia told Reuters Health, “It is important to note that this study is retrospective, and to date no prospective controlled trials have been completed using EBRT for differentiated thyroid cancer.”
“Consequently,” he said by email, “the treatment decisions and grouping of patients in this study are subject to selection bias despite having undergone multidisciplinary review.”
“Use of EBRT for differentiated thyroid cancer is considered somewhat controversial given that specific indications for use are not based on prospectively controlled clinical trial data,” Dr. Fundakowski said. “Many will agree, though, that for advanced T-stage differentiated cancer with significant soft-tissue invasion and high risk of recurrence, EBRT may be appropriate.”
“In the RAI-alone group, tumors with tracheal and esophageal invasion (showed) specifically higher rates of failure compared to tumors with recurrent nerve invasion,” he continued.
“It is important to note though, that 55% of the patients in (that) group with locoregional recurrence did not require additional treatment, and were observed,” he added. “This may provide some argument against the need for EBRT when not all recurrences will require salvage treatment, and additional treatment-related complications may occur with EBRT.”
“Additional prospective studies may provide more clear-cut guidelines and indications for the use of EBRT in differentiated thyroid cancer,” he concluded.
JAMA Otolaryngol Head Neck Surg 2017.
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