False positive ¹⁸F-FDG PET/CT due to gynaecomastia

Excerpt

A 63-year-old male with a history of a melanoma of the left arm (T3N0M0, radically excised) presented with a secondary primary tumour in the nasopharynx. An ¹⁸F-FDG PET/CT scan was performed for staging. Apart from the nasopharyngeal tumour and a cervical node, increased uptake of ¹⁸F-FDG was seen in a corresponding retro-areolar CT lesion in the right breast (a, arrow). This breast lesion was further investigated because of the history of melanoma and the possibility of a third primary breast tumour. A mammogram showed dense tissue behind the nipple of the right breast (b, left). Ultrasound examination revealed retro-areolar heterogeneous tissue (c:N nipple, F fat tissue, P pectoral muscles). No abnormalities were found in the left breast. Although the obtained images were consistent with gynaecomastia, biopsies were performed because of the FDG accumulation and the history of melanoma. Histology (simple HE staining) showed gynaecomastia. The nasopharyngeal carcinoma and cervical metastasis were treated with high-dose conformal radiotherapy (70.2 Gy in 39 fractions of 1.8 Gy) and because of a persistent palpable neck node, a neck dissection was performed 3 months after the last irradiation. In the past 2 years of follow-up the patient has remained free of disease. The breast lesion has not shown any growth. To the best of our knowledge this is the first histologically proven increased accumulation of ¹⁸F-FDG due to gynaecomastia. It is considered a false positive finding in a patient with a history of melanoma. The ability of melanomas to occur as a subcutaneous lesion and the remote possibility of breast cancer, in conjunction with their known glucose avidity, necessitated further analysis [1‐3]. This was done using mammography, ultrasound and biopsy, resulting in the diagnosis of gynaecomastia. No risk factors or possible secondary causes for gynaecomastia were found. In the literature, one case report describes ¹⁸F-FDG accumulation due to bilateral gynaecomastia. However, apart from a ⁶⁷Ga scan it was not validated [4]. When evaluating PET/CT as a staging tool in oncology patients one should consider gynaecomastia as a possible cause for increased uptake of ¹⁸F-FDG in the breast. …