Management of Distant Metastases in Differentiated Thyroid Cancer

Abstract

Follicular cell-derived differentiated thyroid cancer (DTC) is a disease characterized by long-term survival and excellent prognosis. Large-scale studies have defined 10-year survival rates of 85 % in follicular thyroid cancer (FTC) and ~93 % in papillary thyroid cancer (PTC) [1–5]. Despite this, published series report that 6–20 % of patients will develop distant metastatic disease [3, 4, 6–16]. Outcomes in these patients with distant disease are significantly worse, with 10-year survival rates closely approximating 40 % [3, 4, 6, 7, 9, 10, 12–23]. Numerous risk factors have been linked to the development of both regional and distant disease. These include age, tumour size, extrathyroidal extension, multifocality and palpable lymphadenopathy [3, 8, 11, 24]. In 5–45 % of patients, distant disease will be discovered at the time of initial diagnosis on cross-sectional imaging or post-therapy radioactive iodine (RAI) scans [1, 6, 15, 18, 19, 22, 25, 26]. The remainder of patients will develop metastatic recurrence during follow-up. In this latter group, distant disease may be discovered more than 10 years after the initial treatment.

Commentary

Richard W. Nason

Well-differentiated thyroid cancer (WDTC) has a prolonged natural history and a relatively low mortality rate. Recurrence rates approximate 20 % and are most frequently identified in the neck, followed by distant metastases. The most frequent sites of distant metastases are lung and bone. The overall mortality rate for WDTC in North America approximates 10 %. Disease-specific mortality is distributed between local recurrence and distant metastases. The surgeon has some control over the first cause of morbidity and mortality with an adequate initial operation. As emphasized years ago by Dr Crile, the battle of the thyroid is won or lost in the central compartment. Unfortunately, we have less control over this disease in the presence of distant metastases.

As detailed in this chapter, long-term surveillance of patients with WDTC is important to identify both locoregional recurrence and distant metastases. It should be emphasized that follow-up, in my opinion, needs to be directed to the central compartment, as viable treatment options are often available. As indicated in this chapter, young patients with micronodular radioactive iodine (RAI) avid pulmonary metastases do well with treatment. In my experience, older patients with distant metastases are not cured and this does represent a significant source of morbidity and mortality. In our centre, RAI is the treatment if the disease is radio-avid. An important aspect of care in this subset of patients is clinical follow-up with active assessment of symptoms and signs of bone metastases with effective intervention with surgery with or without external beam radiation to minimize pathological fractures or neurological compromise.

The management of patients with distant metastases from WDTC must be individualized and should be based on the circumstances and the experience of a multidisciplinary treatment team. The future for this subset of patients will lie in the development of effective and personalized systemic treatment, as discussed elsewhere in this monograph.