96P Prevalence of hypothyroidism among breast cancer patients treated with radiation to the supraclavicular field: A single center survey

Abstract

Background Radiation-induced hypothyroidism (RIHT) is common complication of head and neck cancer or Hodgkin disease treated with radiation to the thyroid region. However,theeffectofradiationonthethyroidinbreastcancerpatientswhoreceiveda radiation therapy to the supraclavicular (SC) field is unknown. We evaluated the prevalence ofhypothyroidism (HT) in these patients. Methods Between April 2007 and May 2016, consecutive patients with invasive breast cancer who received SC radiation in Kobe City Medical Center General Hospital were recruited. Thyroid-stimulating hormone (TSH), free thyroxine (fT4), anti- thyroglobulin antibody (TgAb) and anti-thyroid peroxidase antibody (TPOAb) were investigatedduringtheperiodofApriltoAugust2016.Basedontheradiationplanning CT-imagesofeachpatient,thevolumeofthethyroidglandwascalculatedanddose- volume parameters were estimated. The primary endpoint was the prevalence ofHT as determinedbyahighserumlevelofTSHandlowserumleveloffT4.Secondary endpointsincludedtheprevalenceofsubclinicalHTasdeterminedbyahighserum level ofTSH andnormal level offT4. Results A total of 68 consecutive patients were screened. Among these patients, 26 were excluded from evaluation (10 patients died, 6 had a history ofprevious thyroid disease, 10werelosttofollowup)andbloodsamplesweretakenin42patients.One(2.4%)and six(14.3%)ofthesepatientshadHTandsubclinicalHT,respectively,withameanTSH levelof8.3mU/ml.Onunivariateanalysis,apossiblepredictivefactorofHTand subclinicalHTwasathyroidvolume<8cm3(OR6.44,95%CI1.13-36.6),incontrast, age, dose-volume parameters, TgAb positivity or TPOAb positivity and follow-up time were not associated with HT or subclinical HT. Conclusions:TheprevalenceofHTinJapanesebreastcancerpatientstreatedwith radiation to the SC region is relatively low compared with that in head and neck cancer and Hodgkin disease patients. Although thyroid volume appeared to be a predictive markerofHTorsubclinicalHTinthiscohort,furtherprospectiveevaluationisneeded. Clinical trial indentification UMIN000022526 release date: June 1, 2016 Legal entity responsible for the study Kobe City Medical Center General Hospital Funding Kobe City Medical Center General Hospital Disclosure All authors have declared no conflicts ofinterest.