Pretargeted radioimmunotherapy in the treatment of metastatic medullary thyroid cancer

Abstract

Medullary thyroid carcinoma (MTC) is a rare cancer (less than 8% of all thyroid cancers) that occurs both as a familial and as a sporadic disease. Total thyroidectomy with dissection of the ipsilateral and central lymph nodes, sometimes extended to contralateral dissection, is the primary treatment of hereditary and sporadic MTC alike. After surgery, many patients are cured, especially those with familial MTC, who are diagnosed early and without metastatic tumour spread. However, some patients show persistent disease after primary surgery, as shown by measurable serum calcitonin.

Three months after surgery, serum calcitonin levels are not detectable in more than 60% of patients without lymph node involvement, as compared with fewer than 20% of patients with lymph node spread. For relapses localized in the neck or mediastinum, a new surgical resection is usually proposed, but this treatment is followed by undetectable levels of serum calcitonin in fewer than one third of patients. The overall survival (OS) rate 10 years after primary surgery in all patients with MTC is 69%, which decreases to 10% when distant metastases are present . Patients with localized or metastatic disease may survive for some years or may rapidly progress and die. Consequently, highly reliable prognostic indicators are needed for the early detection of high-risk patients who require treatment as compared with low-risk patients who warrant a “watch-and-wait” approach. Moreover, these prognostic factors can be very useful in the development of new therapeutic modalities. Here, we consider the most appropriate prognostic indicators and the most efficient imaging techniques for the selection of patients intended to be treated with pretargeted radioimmunotherapy (pRIT). Then, we analyze the effectiveness and toxicity of this new therapeutic modality and compare it with alternative treatments currently available or in evaluation.