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The term “poorly differentiated carcinoma (NOS)” is listed as related to “undifferentiated carcinoma (NOS)” in the ICD-O 3.2. It is also listed in the Solid Tumor Rules for Urinary Table 2 (Urinary subtypes), Other Sites Table 16 (uterine corpus primaries) and Table 19 (vulvar primaries).

Are these the only sites in which one should code “poorly differentiated carcinoma (NOS)” as 8020 (undifferentiated carcinoma)?

How is histology coded if the only microscopic confirmation is from a metastatic site showing “poorly differentiated carcinoma” (NOS) or “invasive carcinoma, poorly differentiated” (NOS)?

Example 1: Primary pancreatic cancer diagnosed on imaging and confirmed with liver mets core biopsy showing “poorly differentiated carcinoma.” Immunostaining pattern was non-specific. No further workup or treatment was planned.

Other Sites - Table 11 (Pancreas Histologies) includes undifferentiated carcinoma (8020/3) as a valid histology; however, the synonyms/subtypes/variants do not mention poorly differentiated carcinoma. How should histology be coded for this case?

Example 2: Hemicolectomy with cecal tumor final diagnosis of “invasive carcinoma, poorly differentiated” and synoptic summary listing “Histologic type: Invasive carcinoma. Histologic grade: G3 of 4: poorly differentiated.”

Colorectal Table 1 (Specific Histologies and Subtypes/Variants) includes undifferentiated adenocarcinoma/carcinoma 8020 as a subtype of adenocarcinoma NOS. There is no mention of poorly differentiated in this context. How should histology be coded for this case?

Patient was diagnosed March 2023 with a neuroendocrine tumorlet of the rectum measuring 0.8 mm via excisional biopsy during colonoscopy.

Prior SINQ 20160011 (stomach specific) indicates microcarcinoid and carcinoid tumors are reportable. Microcarcinoid is a designation for neuroendocrine tumors of the stomach when they are less than 0.5 cm. in size.

Is the current rectal tumor a reportable gastrointestinal neuroendocrine tumor if it is less than 5 mm (i.e., is a neuroendocrine tumorlet equivalent to a microcarcinoid)?

2012 Total abdominal hysterectomy - bilateral salpingo-oophorectomy

Primary Site – Ovary, Right

Histology - Small-Cell Carcinoma (Hypercalcemic Type), Large-Cell Variant

2024 Total abdominal hysterectomy - bilateral salpingo-oophorectomy

Primary Site – Ovary, Left

Histology - Small-Cell Carcinoma (Hypercalcemic Type), Large-Cell Variant

Based on the Solid Tumor Rules, we would make this two since it is over one year. According to a previous SINQ question 20110046, we are to code this as one primary. We see patients come back with multiple carcinoid tumors over the years and would like clarification.

Example: Patient had a 2023 nasopharyngeal mass biopsy showing “Nasopharyngeal non-keratinizing squamous cell carcinoma, undifferentiated type.” 

The Head and Neck Solid Tumor Rules (STRs) do not include an H Rule that instructs us how to code histology when there are two subtypes/variants present for a head and neck primary, nor does the STR define undifferentiated carcinoma as a subtype/variant for 8072.

The WHO Classification of Head and Neck Tumors states non-keratinizing nasopharyngeal carcinoma (non-keratinizing squamous cell carcinoma (SCC) is the most common subtype for nasopharyngeal ca, but that non-keratinizing can be subdivided into undifferentiated and differentiated subtypes.

Should histology be 8020 (undifferentiated carcinoma) or 8072 (non-keratinizing SCC)?

1.  The 2022 and 2023 SEER Program Coding Manuals state under Histologic Type ICD-O-3: Beginning with cases diagnosed 01/01/2022 forward, p16 test results can be used to code squamous cell carcinoma, human papilloma virus (HPV) positive (8085) and squamous cell carcinoma, HPV negative (8086).

NAACCR 2023 Implementation Guidelines contain similar instructions on HPV histologies for cervix, vulva and vagina that are applicable back to 2022 (2021 for cervix).

The current Other Sites Solid Tumor Rules state on the Histology tables for anus, cervix, vagina, vulva, and penis and scrotum: "p16 is a valid test to determine HPV status and can be used to code HPV associated and HPV independent histologies." Since Other Sites Solid Tumor Rules apply to cases diagnosed 2023+, can p16 results only be used from 2023 onward, to code HPV-related histologies for primaries that fall under the Other Sites module? Or per the 2022 SEER Manual statement and NAACCR 2023 Implementation Guidelines, could a p16-confirmed HPV histology code also apply to a 2022 Other Sites case and if so, is that only for cervix, vulva, and vagina? Further complicating the matter are the 2024 ICD-O-3.2 update documents indicating these codes are valid 1/1/2024+ for the “Other Sites” penis and scrotum.

2.  Is using p16 testing for HPV-related histology codes ONLY allowed for sites in the Solid Tumor tables that contain the statements about p16 (Head & Neck Table 5, and the Other Sites tables noted above for anus, cervix, etc.)? Or could it apply to primary sites outside of those tables; for example, a 2022 pathology report from the ethmoid sinus C311 indicating an HPV-related histology based on p16 testing? The ICD-O-3 Annotated Histology lists include C310-C313 among the common site codes for 8085 and 8086. The Head and Neck Solid Tumor Rules “New for 2022” section and rule H1 Note 4 also mention that p16 can be used to code HPV histologies; these sections would seem to apply to all sites in that module, since only the more common histology codes are listed in the tables and if not, we are instructed to use ICD-O.

SEER Program Coding and Staging Manual: Reportability – Reportable Diagnosis List indicates pancreatic intraepithelial neoplasia (PanIN II) (C250-C259) is reportable.

However, the ICD-O-3.2 lists “Glandular intraepithelial neoplasia, grade II” and “Glandular intraepithelial neoplasia, low grade” as histology code 8148 with behavior of /0 (benign).