#1: Solid Tumor Rules (2018, 2021)
Source 1: 2018 Solid Tumor Rules
Notes: Other Sites; For use with cases 2007-2021
Solid Tumor Rules (2018)/Histology--Thyroid: What is the correct histology code for a micropapillary thyroid carcinoma for cases diagnosed 1/1/2021 and later? See Discussion.
The 2021 ICD-O-3.2 Update includes papillary microcarcinoma (8341/3) as the preferred term for thyroid primaries (C739). However, there are multiple SINQ entries instructing registrars not to use code 8341/3 for diagnoses of micropapillary carcinoma of the thyroid (including SINQ 20071076, 20081127, 20110027, 20150023, and 20180008).
SINQ 20150023 specifically indicates: 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 (1 cm 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 carcinoma and codes histology to 8260. If the primary is thyroid and the pathology states papillary microcarcinoma or micropapillary carcinoma, code 8260 is correct.
Does this clarification apply to cases diagnosed 2021 and later? If WHO feels the term micropapillary still does not refer to a specific histologic type for the thyroid, why is 8341/3 listed as a preferred term for this morphology/site combination? For cases 2021 and later, should a diagnosis of Incidental papillary thyroid microcarcinoma (3 mm) in left lower pole, be coded as 8341/3 per the ICD-O-3.2, or as 8260/3 per clarification in multiple SINQ entries?
This question was prompted from preparing SEER*Educate coding exercises. We will use the answer as a reference in the rationales.
Continue to code micropapillary thyroid carcinoma to 8260/3 until instructed otherwise. This coding instruction is based on input from expert endocrine pathologists. This issue will be revisted based on the 4th Ed WHO Endocrine Tumors and updated if needed.