All of the following are helpful for diagnosis of medullary Ca thyroid except -

Important Diagnostic Features of Medullary carcinoma are : Acellular amyloid deposition. Calcitonin secretion by tumour cells. Microscopically polygonal to spindle cell may form nests, trabeculae and even follicles. Electron Microscopy showing variable no. of electron-dense granules (Membrane-bound) within the cytoplasm.