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".

 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

 Finally, someone brought this important differential diagnosis of medullary carcinoma!!!

 This patient's serum Calcitonin is very high according to the endocrinologist. Now, what you need to do?