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The terminology for carcinoid tumors has changed. The current terminology used is "neuroendocrine tumor." Are well-differentiated neuroendocrine tumors of the appendix non-reportable because carcinoid, NOS of the appendix has a borderline behavior code [8240/1]? When the histology/behavior codes for the term "well-differentiated neuroendocrine tumor" became 8240/3, did SEER intend this change to also apply to appendix primaries? If so, for which diagnosis year did this change go into effect?

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?

The term "non-invasive follicular thyroid neoplasm with papillary-like nuclear features" is now being used, instead of the previous classification of an encapsulated malignant thyroid tumor. Recent evidence supports a very minimal risk of aggressive behavior for these tumors, and pathologists in our area are no longer classifying these as malignant in the final diagnosis.

The synoptic report calls this “Invasive adenocarcinoma with secondary Paget disease of anal mucosa and perianal skin.” The tumor size is listed as “2.1 x 1.7 x 0.7 cm, including associated advanced adenoma; size does not include the extent of the associated Paget disease, which extends for at least 2 cm distally.”  Clinically this is called an incidentally discovered Paget’s disease.

It is unclear if this is a collision tumor that should be abstracted as separate primaries, or if this is a single tumor with underlying Paget’s disease (similar to that described in Other Sites Rule H26). If this is a single rectal tumor, there does not appear to be an H rule for this scenario.

The Summary Cancer Data does not seem to describe a more specific histology, but it does describe the tumor histology with the worst outcome and the most extensive tumor. The anaplastic carcinoma grossly extended into skeletal muscle and gave rise to multiple regional lymph node metastases. The more appropriate histology seems to be 8021.

However, current MP/H Rules for a single tumor indicate the histology should be coded to the numerically higher histology code (8260). Coding the histology to 8260 does not account for the more aggressive tumor. Should this histology be 8260 or 8021?

The STR states that p16 can be used to code HPV-associated and HPV-independent histologies for selected sites depending on diagnosis year but contains no instructions about how to interpret p16 staining results on pathology reports. These are often stated in various ways in our area, depending on the pathology lab and different pathologists. The SSDI Manual and SEER Coding and Staging Manual each have some instructions and code definitions for p16, including:

- Code 0 for p16 expression of weak intensity or limited distribution

- Code 0: p16 Negative; Nonreactive

- Code 1: p16 Positive; Diffuse, Strong reactivity

- IHC for p16 expression is a surrogate marker for HPV infection

Example: 2023 squamous cell carcinoma of the vulva, partial vulvectomy; pathology states vulvar intraepithelial neoplasia-3, p16 immunohistochemistry demonstrates block-like expression, which supports the diagnosis. The next path report states invasive squamous cell carcinoma, stain for p16 is strong and diffuse in the lesion, supporting the above diagnosis. Neither path report specifically states "HPV-related," so are p16 "expression" and "strong and diffuse" staining enough to code the histology as 8085/3 for this case?

The Solid Tumor Rules state that for cases diagnosed in 2022 and forward, p16 testing CAN be used to assign histology code 8085 (squamous cell carcinoma, HPV positive). The rules also state that for cases diagnosed prior to 1/1/2022, code 8085 MUST be based on ISH testing and not p16. ISH testing is not specifically addressed for 2022+ cases, but are we correct in assuming it can still be used as the basis for 8085?

Multiple CAnswer Forum posts and the AJCC 8th edition Head and Neck staging webinar indicate that the correct chapter/registry staging schema in this situation is determined ONLY by p16 results - not ISH testing, and therefore the Schema Discriminator 2 SSDI should be coded as 1 – p16 negative, regardless of ISH results.

While we understand that histology codes should not be changed based on staging criteria, there is a SEER/NAACCR edit, “Schema Discriminator 2, Head and Neck, Histology (NAACCR)” tag number N6802, that will not allow coding 8085 if Schema Discriminator 2 is coded as 1 (p16 negative). The edit does seem to be correctly enforcing the AJCC guidelines for choosing the staging schema, based on the sources noted above. Do the Solid Tumor or Site-Specific Data Items (SSDI) guidelines need to be modified for this situation?

The Solid Tumor Rules instruct us not to use differentiation for coding histology unless it is specifically listed in the table. The terminology non-small cell carcinoma with neuroendocrine differentiation is not in lung histology Table 2.

However, SINQ 20150033, prior to Solid Tumor rules, indicates this diagnosis should be coded to 8574 (adenocarcinoma/carcinoma with neuroendocrine differentiation).

This presentation appears to represent distinctly different histologies. However, because the 2018 histology diagnosis is not in the table and the prior SINQ appears to disagree with current instruction, it is not clear how to apply the M rules to this case. The outcome of the histology coding will affect the number of primaries reported in this case.

The Solid Tumor Rules indicate p16 is a valid test to determine HPV status and can be used to code HPV-associated/-independent.

In this case, we do not know whether the HR-HPV test was done on cytologically malignant cells, or on benign cervical cells. It may be impossible to tell unless 100% of the cytology specimen is malignant, but we will not have access to that information. Also, HR-HPV testing is routine on Pap smears, so this testing does not mean the tumor cells specifically harbor HPV.

The Solid Tumor Rules indicate bladder tumors that are urothelial carcinoma (8120) and small cell carcinoma (8041) are separate primaries per Rule M13 (Abstract multiple primaries when separate/non-contiguous tumors are on different rows in Table 2). These are distinctly different histologies and, presumably, one would want to capture the small cell carcinoma (or small cell carcinoma component) as this has a worse prognosis.

However, if a subsequent bladder tumor is composed of invasive urothelial carcinoma and small cell neuroendocrine carcinoma, the histology is coded as 8045/3 per Rule H4, but this is not abstracted as a multiple primary. The only M Rule that applies is Rule M18 (Abstract a single primary when tumors do not meet any of the above criteria). The mixed histology code 8045 is not included in Table 2, so none of the histology-based M Rules apply. Is the subsequent mixed invasive urothelial and small cell carcinoma tumor (8045/3) the same primary as a previously diagnosed invasive urothelial carcinoma (8120/3) when these tumors are diagnosed within three years?