The patient in this case had history of FTC thyroidectomy. Unlike primary breast carcinoma, architectural distortion, calcification, posterior acoustic shadowing, spiculated margins, and skin or nipple retraction are infrequent in breast metastatic lesions on mammography and ultrasound. The involvement of axillary lymph node is also less common in metastatic lesions than in primary breast cancer [10, 11]. However, in this case, the imaging presentation of breast metastasis was accompanied by distortion and calcification of the surrounding glands, which was not entirely consistent with conventional mammography findings. Therefore, mammography and ultrasound alone do not completely explain the secondary nature of breast malignancy.
This patient’s PET/CT showed FDG signal in the thyroid region, lung, and breast lesion. Because of the patient’s history of FTC thyroidectomy, the probability of a final diagnosis of FTC metastasis to the lung and breast using PET/CT is relatively high [4, 12]. PET/CT is not specific for the diagnosis of breast lesions, as it cannot be used to determine whether a breast lesion is a metastasis or a primary lesion based on SUVmax alone [10]. A history of thyroidectomy can render the evidence of PET/CT more reliable for the diagnosis of FTC breast metastasis. Previous studies have reported similar cases of FTC breast metastasis confirmed by PET/CT findings and postoperative pathology [4, 5]. Therefore, a thyroid-related disease history is important for the diagnosis of FTC breast metastasis.
For the treatment of DTC, National Comprehensive Cancer Network and American Thyroid Association guidelines typically recommend total thyroidectomy, TSH suppression therapy, and I-131 radioablation for patients at high risk of recurrence. However, persistence/recurrence still occurs in 20–30% of these patients [13].
In this case, the patient was not treated with I-131 radioablation and TSH suppression after the initial subtotal thyroidectomy. Expert consensus or recommended treatment options for metastasis to the breast, a rare metastatic site, is lacking. We decided to adopt a regimen of total thyroidectomy and segmental mastectomy, followed by I-131 radioablation for this patient. This is because of several reasons: first, the prognosis of FTC is relatively worse than that of PTC [14]; second, unlike FTC, which is limited to the thyroid or cervical lymph nodes, the average 5-year overall survival rate for patients with distant metastases is generally reduced to 50% [13]; third, FDG-positive lesions on PET images usually indicate undifferentiated changes in FTC lesions, indicating relatively poor prognosis for FTC. Therefore, we believe that the efficacy of I-131 radioablation alone for the treatment of breast metastasis is not significant, and local surgical excision of recurrent foci and metastasis should be performed first. As this patient had metastasis, incomplete tumor resection or high-risk continued radioiodine therapy and TSH suppression therapy were definitely indicated. Unfortunately, I-131 whole-body imaging was not performed before mastectomy for breast metastasis in this case. Total thyroidectomy, segmental mastectomy, I-131 radioablation, and TSH suppression therapy enabled CR of the recurrent FTC foci and breast metastasis in a relatively short period of time. Thus, this case revealed a reliable treatment option for breast metastases from FTC.
The main limitation of our case report is that we did not perform I-131 whole-body imaging before mastectomy for breast metastasis, which could have provided more information on the extent and distribution of the metastatic lesions. The main implication of our case report is that it provides a valuable reference for the diagnosis and treatment of breast metastasis from FTC, which is a rare but possible complication of thyroid cancer. We report a case of FTC breast metastasis that occurred 17 years after subtotal thyroidectomy, which is an exceptionally long interval compared to previous reports [4, 6]. This suggests that long-term follow-up and surveillance are necessary for patients with FTC, especially those with incomplete tumor resection or high-risk features. Clinicians should be aware of the possibility of breast metastasis from FTC in patients with a history of thyroid cancer, especially if they present with a new breast mass or pain. Radiologists should also consider breast metastasis from FTC in the differential diagnosis of breast lesions, especially if they show discordant iodine and FDG uptake on functional imaging. A prompt diagnosis is crucial to avoid unnecessary or inappropriate interventions and to initiate adequate treatment.