3.1.2. Metastasectomy (Complete Resection of the Tumor)

Generally, BMs from DTC are more resistant to radiotherapy and systemic therapy than other metastases [2,43]. A significant proportion of patients with DTC-BM in the spine, which is the site most affected by DTC-BM, have a solitary spinal lesion without non-spinal BMs or other organ metastases [5]. Based on these factors, skeletal lesions from DTC have the best indication for metastasectomy, if feasible. Surgery is intended to improve or maintain the QOL and PS over a long-term period and to prolong survival [5]. Since the 2000s, metastasectomy for DTC-BM has been reported to be a significant factor associated with improved survival rates [20,44,45]. The guidelines state that complete resection of BMs can prolong survival and is particularly appropriate for younger patients [1,46]. Moreover, the declining performance of daily activities and neurological deficits caused by BMs make it difficult for patients to undergo RAI therapy, which is the mainstay of treatment for metastases, especially in vital organ lesions, from DTC. Thus, metastasectomy of skeletal lesions, if achievable, should be considered. This aggressive surgery can be applied to patients with metastases from DTC because of its unique characteristics, mentioned above, and its favorable prognosis. The treatment strategy for thyroid BMs is therefore different from that for BMs from other malignancies.

Table 1 presents studies of surgery for BM from thyroid carcinoma, mainly DTC, with detailed clinical results, including information about postoperative survival and/or local tumor control in the operated lesions [9,47–52]. To reflect the most contemporary practice, only studies published in the last 10 years are included. However, there are few comparative studies on complete and incomplete excision of DTC-BM [9,47,48]. The postoperative survival rate of patients undergoing metastasectomy was more favorable, with lower local recurrence rates, than that of patients who underwent incomplete excision [47,48]. Kato et al. examined the minimum 4-year postoperative outcomes for patients who underwent surgery for spinal lesions and reported that only one patient who underwent complete excision experienced local tumor recurrence in the operated spine, whereas all long-term survivors (>18 months after surgery) in the incomplete excision group experienced local tumor recurrence and a consequent deterioration of PS [48]. Satcher et al. examined the clinical outcomes for patients who underwent surgery for appendicular skeletal lesions; after adjusting for age and sex, they reported that patients who had their tumor excised or presented with solitary bone involvement had a lower risk of death [49]. Yin et al. examined the clinical outcomes for patients with BMs in the cervical spine, which severely compromised the PS of the patients; they reported that the strongest factor in improved survival rates after the diagnosis of cervical spine metastasis was local disease control of the lesion, and that surgical intervention was significantly associated with improved survival [52].



BM, bone metastasis; Ex, excision; F, female; FTC, follicular thyroid carcinoma; FU, follow-up; LC, local control; LR, local recurrence; M, male; N/A, not available; No., number; PTC, papillary thyroid carcinoma; pub., publication.

> Excisional surgery for BMs, especially in the spine, is a remarkable and technically demanding surgery for general orthopedic and spine surgeons because the metastases are hypervascular and destructive, and reconstruction to support the operated lesion against load is required after tumor resection in most cases. Although it is not always feasible, complete resection of macroscopically identified bone tumor is recommended, and a favorable outcome has been reported even in patients with coexisting controlled lung metastases (Figure 1) [48]. Isolated and resectable BMs from kidney cancer are also indicated for metastasectomy. A simple and tailored treatment algorithm for spinal metastases from these two cancers has been reported [53], and it can be adapted for nonspinal BMs.
