Thyroid cancer presenting as a PET incidentaloma in a patient with concomitant breast cancer metastases to the thyroid.

INTRODUCTION: Metastases to the thyroid gland are considered a rare cause of thyroid tumor. Furthermore, a relationship between breast and thyroid carcinoma has been previously proposed.

CASE DESCRIPTION: We describe the case of a 59-year-old woman who presented with simultaneous papillary and breast carcinoma within the thyroid gland. F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) done for the evaluation of her metastatic breast cancer revealed a thyroid incidentaloma with a high metabolic rate (standardized uptake value [SUV] of 13). She underwent thyroidectomy and the pathology revealed papillary thyroid carcinoma corresponding to the lesion visualized on FDG PET. However, small metastatic implants of breast carcinoma were seen within the opposite thyroid lobe.

CONCLUSION: This is a rare description of a concomitant papillary thyroid carcinoma presenting as an FDG PET incidentaloma alongside breast cancer metastases to the thyroid gland. Thyroid and breast cancer sometimes occur in the same patient. However, no explanation has been found to link these 2 cancers. Although uncommon, FDG PET thyroid incidentalomas seem to harbor a higher rate of malignancy than incidentalomas found on conventional imaging. In the appropriate clinical setting, it is therefore suggested to investigate these lesions thoroughly.