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Code to papillary carcinoma, encapsulated (C73.9) (8343/3) using Solid Tumor Rules, Other Sites, Rule H11, code the histology when only one histologic type is identified.  The usage of features is describing the cellular architecture of the encapsulated papillary carcinoma and does not necessarily indicate a specific histologic type. We consulted with our endocrine specialist pathologist who agrees and indicated terminology used in thryoid neoplasms is inconsistent.

Code papillary carcinoma, tall cell variant with oncocytic features to papillary carcinoma, tall cell (C73.9) (8344/3).  The WHO Classification of Endocrine Organs states that this variant is composed of cells that are as tall as they are wide, and show abundant eosinophilic (oncocytic-like) cytoplasm.  Tall cells must account for greater than or equal to 30% of all tumor cells.

Per the WHO Tumors of Endocrine Organs, for thyroid primaries/cancer only, the term micropapillary does not refer to a specific histologic type. It means that the papillary portion of the tumor is minimal or occult (1cm or less in diameter) and was found incidentally. WHO does not recognize the code 8341 and classifies papillary microcarcinoma of the thyroid as a variant of papillary thyroid and thereby should be coded to 8260. If the primary is thyroid and the pathology states papillary microcarcinoma or micropapillary carcinoma, code 8260 is correct. This information will be included in the upcoming revisions to the MP/H manual.                        

For tumors diagnosed prior to 2007:

Yes, this is a second primary. The second papillary carcinoma was more than 2 months after the first and not specified as recurrent or metastatic.

For tumors diagnosed 2007 or later, refer to the MP/H rules. If there are still questions about how this type of tumor should be coded, submit a new question to SINQ and include the difficulties you are encountering in applying the MP/H rules.

Assign histology as 8340/3 for IEFVPTC using the STR Manual, 2026 Update. Rule M18, Note 2, of the Other Sites STR state: Invasive encapsulated follicular variant of papillary thyroid carcinoma and Infiltrative follicular variant of papillary thyroid carcinoma share a histology code (8340) but are distinctly different entities. They are on separate rows of the table.

WHO Classification of Endocrine and Neuroendocrine Tumors, 5th ed., indicates that after classic PTC, the follicular variant of PTC (FVPTC) is the second most common histological subtype of PTC. Two major forms are known, infiltrative FVPTC and invasive encapsulated FVPTC. The majority of follicular PTCs are encapsulated FVPTCs, whereas infiltrative FVPTC is quite rare and clinically behaves like classic PTC.

Do not report angioinvasive oncocytic thyroid neoplasm with features worrisome for a poorly differentiated oncocytic carcinoma based on the final, unchanged diagnosis.  Worrisome is not a reportable ambiguous terminology.

For tumors diagnosed prior to 2007:

Code the Histology field to 8507/3 [micropapillary carcinoma]. According to rule H, the topography code listed in the ICD-O is disregarded if the tumor is known to arise in another site. In this case, the site is thyroid [C73.9] so the topography code of breast [C50._] can be disregarded for this histology. Apply the matrix principle to change the Behavior Code from 2 to 3.

For tumors diagnosed 2007 or later, refer to the MP/H rules. If there are still questions about how this type of tumor should be coded, submit a new question to SINQ and include the difficulties you are encountering in applying the MP/H rules.

Code Hormone therapy as 01 [Hormone therapy administered as first course therapy] when thyroid replacement therapy is part of the first course of treatment for follicular or papillary thyroid cancer following thyroidectomy.

Thyroid hormone replacement therapy has a treatment effect on differentiated (follicular and papillary) carcinomas of the thyroid. This treatment effect is not seen for most medullary and undifferentiated thyroid cancers.

Without evidence of a new testicular tumor, record this as a single primary now with metastatic disease (seminoma). The seminoma may not have been identified in the original tumor and treatment was based on the histologies found. This allowed the seminoma to metastasize.