CALCA and medullary thyroid gland carcinoma: However, these rarely may be present in other benign and malignant conditions including medullary carcinoma, follicular carcinoma and Hurthle cell carcinoma and hence caution should be exercised, especially when these features are present focally.[16–19] Although demonstration of calcitonin and CEA positive tumor cells using immunohistochemical stains can further support the diagnosis of medullary carcinoma, negative staining does not exclude the diagnosis.