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This case was signed out by one of our pathologists as "Thyroid neoplasm, favor papillary thyroid carcinoma", then the clinician called her and mentioned the high serum Calcitonin. Then the pathologist did a cell block and did immunostains for CEA and calcitonin and amended the report to "thyroid neoplasm, favor medullary carcinoma".
I learned a great deal from this case. Medullary thyroid carcinoma has a nickname "melanoma of the thyroid", because it can mimic many thyroid neoplasm. The general rule I learned from my cytopathology fellowship is that if a thyroid neoplasm looks not perfect for papillary carcinoma, follicular neoplasm, or Hurthle cell neoplasm, think about medullary carcinoma.
Now, I list a good table of differential diagnosis of papillary carcinoma (PTC) vs. medullary carcinoma (MTC) from Dr. Kini's book of thyroid FNA
MTC PTC
Cellularity Highly cellular Highly cellular
Cells Cells mostly in dispersed pattern Cells mostly in groups, syncytial
rarely in syncytial pattern pattern, rarely dispersed pattern
Nucleus Eccentric, salt- and -pepper chromatin Eccentric to central, can have salt
binucleation frequent, nuclear pseudo- -pepper chromatin, binucleation
inclusion can be seen Not a feature, pseudo-inclusion
is always seen
Cytoplasm Scant to variable, pale to dense Variable, pale clear or vacuolated
Background Colloid absent, amyloid present can have colloid, amyloid absent
Immunoprofile Calcitonin +, Thyroglobulin - Calcitonin-, thyroglobulin +
Hopefully this discussion will be interesting to you
Thank you so much 月新 for the translation. Just to follow-up on this case. the patient had surgery last Friday and I have the surgical pathology. It is medullary carcinoma, but has some unusual features, like psammoma bodies and focal follicular differentiation. I am posting one photo of the histology and one photo of the immunostain for calcitonin.
This case also raises the possibility of a combined papillary and medullary carcinoma, but the thyroglobulin stain is completely negative. Thus, at the end, I feel it is better to classify the whole tumor as medullary carcinoma.
Hope this case illustrates that medullary carcinoma can have many "faces".