Table 1.
Prospectus of the included studies
| Author | Reference | Journal | Year |
|---|---|---|---|
| Sobol RE | Hormone-negative, chromogranin A-positive endocrine tumors. | New England Journal of Medicine | 1989 |
| Schmid KW | “Atypical” medullary thyroid carcinoma with little or no calcitonin expression. | Virchows Archive A Pathological Anatomy and Histopathology | 1998 |
| Redding AH | Normal preoperative calcitonin levels do not always exclude medullary thyroid carcinoma in patients with large palpable thyroid masses. | Thyroid | 2000 |
| Bockhorn M | Lack of elevated serum carcinoembryonic antigen and calcitonin in medullary thyroid carcinoma. | Thyroid | 2004 |
| Sand M | Serum calcitonin negative medullary thyroid carcinoma. | World journal of surgical oncology. | 2006 |
| Dora JM | Normal perioperative serum calcitonin levels in patients with advanced medullary thyroid carcinoma: case report and review of the literature. | Thyroid | 2008 |
| Wang TS | Medullary thyroid carcinoma without marked elevation of calcitonin: a diagnostic and surveillance dilemma. | Thyroid | 2008 |
| Giovanella L | Serum calcitonin-negative medullary thyroid carcinoma: role of CgA and CEA as complementary markers. | The International Journal of Biological Markers | 2008 |
| Alapat DV | Disparity between tissue and serum calcitonin and CEA in patient with medullary thyroid carcinoma. | Endocrine | 2011 |
| Chernyavsky VS | Calcitonin-negative neuroendocrine tumor of the thyroid: a distinct clinical entity. | Thyroid | 2011 |
| Nakazawa T | C-cell-derived calcitonin-free neuroendocrine carcinoma of the thyroid: the diagnostic importance of CGRP immunoreactivity. | International journal of surgical pathology. | 2011 |
| Frank-Raue K | Prevalence and clinical spectrum of nonsecretory medullary thyroid carcinoma in a series of 839 patients with sporadic medullary thyroid carcinoma. | Thyroid | 2013 |
| Ismi O | Calcitonin-negative neuroendocrine tumor of thyroid gland mimicking anaplastic carcinoma: an unusual entity. | Gland Surgery | 2014 |
| Brutsaert EF | Medullary thyroid cancer with undetectable serum calcitonin. | The Journal of clinical endocrinology and metabolism. | 2014 |
| Kim JY | A calcitonin-negative neuroendocrine tumor derived from follicular lesions of the thyroid. | Endocrinology and metabolism. | 2015 |
| Kasajima A | A Calcitonin Non-producing Neuroendocrine Tumor of the Thyroid Gland. | Endocrine pathology. | 2016 |
| Samà MT | Clinical challenges with calcitonin-negative medullary thyroid carcinoma. | Journal of cancer research and clinical oncology | 2016 |
| Parmer M | Calcitonin-Negative Neuroendocrine Tumor of the Thyroid. | International journal of surgical pathology. | 2017 |
| Zhou Q | Clinical and pathological analysis of 19 cases of medullary thyroid carcinoma without an increase in calcitonin. | Experimental and toxicologic pathology: official journal of the Gesellschaft für Toxikologische Pathologie. | 2017 |