Short summary

To evaluate the risk of hypothyroidism after nodal irradiation for early-stage breast cancer. We will conduct a prospective study to compare thyroid function before and after RT, estimating the actual radiation dose to the thyroid by delineating the thyroid from compute tomography (CT) scans, and determining when breast cancer patients are most likely to develop sub-clinical or overt hypothyroidism after RT.

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Rationale

Breast cancer is the most common malignant disease among women worldwide. Today, close to 90% of patients with early-stage breast cancer receive adjuvant treatment (chemotherapy, anti-HER-2-therapy, endocrine therapy, or RT. As breast cancer survival improves, understanding the late effects of this disease and its treatments becomes increasingly important.

Hypothyroidism is a well-documented late effect of RT for head and neck cancer. It manifests months to years after RT and requires life-long substitution therapy. Breast cancer patients who receive RT - especially to the supraclavicular region - may also be at higher risk for hypothyroidism. Studies on the incidence of hypothyroidism in breast cancer survivors, however, have been small, or confined to elderly patients, and therefore lack generalizability. The previous research on incidence of hypothyroidism in breast cancer was based on hypothyroid diagnoses only and failed to incorporate treatment of the disease. As hypothyroidism warrants thyroxine supplementation for life, and patients can be treated outside hospital, the incidence of hypothyroidism in breast cancer survivors is likely underestimated. Our aim is to explore in a feasibility study, the potential dose-dependent effect of RT on the incidence of hypothyroidism in breast cancer patients.

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Description of the cohort

A prospective study of 150 women diagnosed with early-stage operable breast cancer at Odense University Hospital (OUH), Denmark, between 01/03/2015 and 31/02/2018. We will recruit 100 patients eligible for locoregional RT (to the breast and regional lymph nodes) and 50 eligible for local RT (to the breast only) or without RT. 

Data and biological material

Patients that participate in the study will give blood samples before adjuvant therapy, and after treatment at their routine 6, 12, and 18 month follow-up exams. Thyroid function (TSH, FT4, and baseline anti-TPO) will be measured.

Radiotherapy is CT-guided. We will retrieve RT dose plans for all RT-treated patients, delineate the thyroid and estimate the RT dose to the thyroid.

Collaborating researchers and departments

Department of Clinical Epidemiology, Aarhus University Hospital

• Associate Professor Deirdre Cronin Fenton, PhD

Department of Oncology, Odense University Hospital

• Professor Marianne Ewertz
• Clinical Oncologist Jeanette D. Jensen
• postdoctoral physicist Ebbe L. Lørenzen

Department of Endocrinology, Leiden University Hospital, Netherlands

• Endocrinologist and Epidemiologist Olaf M. Dekkers

Department of Oncology, Oslo University Hospital, Norway

• Oncologist Kristin V. Reinertsen