Endocrine Abstracts

Introduction: Medullary thyroid carcinoma (MTC) in multiple endocrine neoplasia type 2B (MEN2B) syndrome is associated with RET mutation. Patients harbouring de novo mutations are usually diagnosed in more advanced stages of the disease. We present the case of a young female patient with MEN2B diagnosed with stage IV medullary thyroid carcinoma at the age of 10 years.

Aim: Characterizing the efficacy of the different sequences of therapies and disease progression by calculating calcitonin doubling rates based on serial calcitonin measurements.

Methods: Different phases of spontaneous tumor development, the efficacy of surgical interventions and individual drug treatment intervals were analyzed with calcitonin doubling rates (Ct-DR).

Results: De novo mutation involving the Met918Thr in exon 16 of the RET proto-oncogene confirmed the genetic background of the disease in our patient. In 2006-2015, she underwent four operations. We found a less steep increase in log-transformed calcitonin levels after the first compared to subsequent operations. A significant drop in serum calcitonin after a pheochromocytoma removal was suggestive of calcitonin secretion, confirmed by subsequent immunohistochemical analysis. After suffering multiple surgical interventions for local and regional recurrence, the disease still progressed, leading to metastatic disease in the fifth year after diagnosis. The patient underwent five different types of TKI treatment (sunitinib, vandetanib, cabozantinib, lenvatinib, and selpercatinib), with different responses and multiple adverse effects. Three of the five TKIs resulted in an immediate drop of serum calcitonin followed by significantly less steep increases than untreated periods for vandetanib and selpercatinib. Even after the initial drop in calcitonin, we found a continuously decreasing calcitonin trajectory for selpercatinib. Sunitinib and cabozantinib had to be discontinued due to severe side effects. Vandetanib was used for the longest time, slowing the progression of the disease, and causing tolarable adverse events. The best treatment response, as reflected by negative Ct-DR and lack of side effects, was observed with selpercatinib, granting a stable disease and improving quality of life after 17 years from diagnosis.

Conclusion: Our case illustrates the long-term survival of a young MEN-2B patient diagnosed with advanced medullary thyroid carcinoma. The case presents how the effectiveness of different treatment modalities can be approached using log-transformed calcitonin levels.