[Papillary thyroid carcinoma synchronous with breast cancer: an incidental finding in an (18)F-FDG PET-CT study carried out in a search for occult breast cancer].

The most common cause of metastatic involvement of axillary lymph nodes in women is ipsilateral breast cancer. The definition of occult breast malignancy has changed over time. Nowadays, it is considered to exist when it coincides with an isolated metastatic axillary abnormal lymph node in the absence of a palpable tumor in the ipsilateral breast, non-diagnostic breast tumor mammography and no detection of other malignancies outside the breast which could potentially affect the axillary nodes. The value of (18)F-FDG PET/CT scan in these patients has not been established, but it could be useful in those patients with a non-diagnostic MRI. It is not uncommon in (18)F-FDG PET/CT studies to identify incidental hypermetabolic focal image in the thyroid. The high prevalence of cancer in these lesions makes it recommendable to perform a US study and/or FNAP biopsy.