SAT568 A Case Of Medullary Thyroid Cancer Associated With Cutaneous Metastasis: A Rare And Aggressive Presentation
Authors: Vaghasia Nishit , Hasan Farhad , Grimes Michael 
Published: October 2023

Abstract
Disclosure: N. Vaghasia: None. F. Hasan: None. M. Grimes: None.
Introduction: Cutaneous metastasis (CM) is an extremely rare site of metastasis in medullary thyroid cancer (MTC). It suggests aggressive malignancy and poor prognosis in most cases.
Case: A 26 year old male with no PMH presented to ER with neck discomfort and lump noted few weeks prior to presentation. Neck examination revealed a tender left uninodular goiter. Thyroid US revealed a 7.1 cm solid, hypoechoic, lobular, taller than wide left thyroid nodule with macrocalcification and two abnormal appearing level 2 and 3 left cervical lymph nodes. FNA of all three lesions were positive for MTC. CT neck and PET scan suggested locally advanced tumor surrounding carotid artery and esophagus plus metastatic lesion in the pelvis. Interestingly, serum calcitonin was only modestly elevated at 28.9 pg/ml (0.0-8.4), while serum CEA was high at 8.7 ng/mL (0-3.0). Genetic testing for germline RET mutation was negative. Patient underwent a total thyroidectomy with central and left lateral neck dissection and pelvic mass resection with pathology revealing MTC, stage T4b N1b M1. Molecular testing was negative for RET mutation. Patient underwent EBRT of the neck for residual disease after surgery. Patient was started on Cabozantinib therapy. Seven months after initial presentation, he had new skin lesions, one on scalp and two on left lateral chest wall described as 1-2 cm cystic papular lesion, reddish-yellow in color and tender to palpation. Excision of all three lesions were positive for MTC confirming CM. Patient’s most recent PET scan suggested residual disease in the neck and new metastatic lesion in the right humerus. Patient’s serum calcitonin level remained within the reference range after surgery despite residual disease.
Discussion: MTC with CM is extremely rare with fewer than 10 reported cases. Most of them are associated with high mortality with death within one year from diagnosis. Most of the cases had skin lesions in upper body with scalp being the most common site. Not much is known about the molecular profiling of MTC with CM. Our case is similar to previously reported cases in terms of disease aggressiveness and skin lesions involving the scalp and upper chest. Two unique features about our case are: first, the modest elevation of calcitonin preoperatively despite large tumor burden and normal calcitonin after surgery despite having residual disease and new distant metastasis. Second, molecular profiling of our patient was negative for germline mutations in association with MTC. This may suggest the presence of an unknown mutation or pathway leading to this unusual manifestation in MTC.
Conclusion: In a patient with known MTC, skin lesions especially on scalp should raise suspicion for metastatic and aggressive MTC. With minimally elevated calcitonin and negative RET mutation our case raise one important question - Is a normal calcitonin and negative RET oncogene associated with an aggressive form of MTC?
Presentation: Saturday, June 17, 2023