Biochemical and Genomic Changes of a Devastating Metastatic Medullary Thyroid Cancer

Abstract

Abstract Introduction: Medullary thyroid carcinoma (MTC) is a neuroendocrine tumor of thyroid parafollicular C cells. About 25% of cases are hereditary, associated with MEN2 syndromes. RET M918 mutation (somatic or germline) is associated with the most aggressive form of MTC. If MTC is hereditary, further tumor genomic analysis is not routinely performed. Therefore, the somatic mutational landscape of hereditary MTCs is not frequently described in the literature. We present an unusual case of MTC with a germline M918 RET mutation, displaying an initial smoldering course followed by rapidly fatal widespread metastases. Whole exome sequencing (WES) of primary tumor and metastases revealed intertumoral heterogeneity with many somatic mutations including p53 mutation. Clinical Case: The patient with characteristic facies of MEN 2B presented with a neck mass at age 28. She had no family history of MEN. At diagnosis, calcitonin was 11,392 pg/mL and CEA was 729.7 ug/L. Pathology showed MTCs of 5 cm (right) and 2.1 cm (left) with lymph node metastases (pT3N1bMx). Genetic testing showed RET M918 mutation. Postoperative calcitonin and CEA were 3.3 pg/ml and 1.7 ug/L respectively. Tumor markers doubling time was initially about 1 year, but progressively shortened over time. Three years after surgery, calcitonin and CEA were 101 pg/ml and 387 ug/L respectively. CT chest and abdomen identified no distant metastasis. Over the next 4 months, calcitonin and CEA increased dramatically to 1821pg/ml and 3974 ug/L. The patient was admitted for acute liver failure and passed away. Autopsy revealed widely metastatic disease to liver, lungs, spleen, pituitary, right adrenal gland, bones, and brain. WES revealed 87, 283 and 591 somatic mutations in the primary tumor, lung and liver metastases respectively. The primary tumor had chromosome 1p loss whereas liver and lung metastases had somatic mutation of TP53 and single copy loss of chromosome 17 (biallelic inactivation of p53). Conclusion: This case illustrates intertumoral spatial and temporal genetic heterogeneity. Mutations detected by WES may or may not be cancer-related and their clinical relevance is often uncelar. We hypothesize TP53 biallelic loss might have contributed to the aggressive phenotype of this tumor. Also of note, even before the appearance of metastases, CEA was disproportionately higher than calcitonin, reflecting tumor dedifferentiation. Further studies are needed to address CEA threshold for additional imaging and imaging modality for early detection of metastases.