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HGAP is listed as a separate classification and is not a subtype of the diffuse gliomas. WHO Classification of Tumors of the Central Nervous System, 5th edition, has two categories dealing with non-pediatric astrocytic tumors:

Adult-type diffuse gliomas

Circumscribed astrocytic tumors

HGAP falls into the second category as a result of updates to the 4th edition WHO classification in 2016 with advances in the role of molecular diagnostics with the 5th edition. All astrocytic tumors were previously grouped together whereas not all diffuse gliomas (astrocytic or not) are grouped together on the basis of growth pattern and behaviors, and shared IDH1 and IDH2 genetic status. The new classification separates astrocytomas that have a more circumscribed growth pattern, lack IDH gene alterations, and sometimes have BRAF mutations (i.e., pilocytic astrocytoma). The impact of molecular advances has driven classification changes as described in the 5th edition.

Review of site/histologiy combinations for CNS neoplasms is currently being performed by Cancer PathCHART experts. It's possible they will recommend HGAP be moved to a subtype/variant of astrocytoma, NOS. 

The CPC ICD-O-3 Site Morphology Validation Lists (SMVLs) designate all tumor site-morphology combinations that are either valid or impossible as determined for the sites reviewed by the Cancer PathCHART initiative. These lists provide information on the Validity Status of specific tumor site and morphology combinations, similar to the way the ICD-O-3 SEER Site/Histology Validation List used to. However, the CPC SMVLs do not include information on the reportability of specific tumor site and morphology combinations. For tumor reportability, you will continue to use the Excel ICD-O-3.2 spreadsheets posted to the NAACCR ICD-O-3 Coding Updates website: https://www.naaccr.org/icdo3/, and the most recent SEER Manual and federal, state, local, and other standard setters' reportability requirements.

Assign the highest code with 51 as the highest and 10 the lowest when there is more than one test performed with differing results.

The SEER Manual will be updated in the 2025 release. SEER*RSA will be updated in a future release, version 3.3 in 2026, as version 3.2 has been updated for 2025.

The correct term is diffuse leptomeningeal glioneuronal tumor listed as a synonym in Column 2. 

We will add the term diffuse in Note 2, Column 1 with the 2025 updates. In the meantime, you can add "diffuse" to your pdf version until the update is published.

High grade dysplasia of the esophagus is reportable. The example will be corrected in the next edition of the SEER manual.

Assign 8230/2 (ductal carcinoma in situ, solid type/intraductal carcinoma, solid type) using Breast Solid Tumor Rules Table 3 as instructed in Rule H2 for in situ tumors. The carcinoma, NST row lists this histology in the subtype/variant column 3.

Coding histology for in situ breast tumor differs from invasive. While the majority of in situ breast primaries will be coded to DCIS 8500/2, there are others that are listed in Table 3 that should be coded according to the specific histology. Some codes have the word subtype or type as part of their histologic term so these can be coded based on the histologic term as listed in the table. We suggest you routinely review the histology tables to see if a term is listed.

Assign code 2, Neoadjuvant therapy started, but not completed OR unknown if completed, for the 2024 SEER Manual data item Neoadjuvant Therapy. Assign code 2 when neoadjuvant therapy was begun and the patient did not complete the full course of neoadjuvant therapy. See Coding Instruction #3 on page 230. The fact that the patient completed five cycles of the planned chemotherapy, but the sixth cycle was held due to neutropenia is important information and should be abstracted correctly and documented via text data items.

Assign histology as DLBCL (9680/3) as supported by the WHO Classification of Hematolymphoid Tumors, 5th edition. It is consistent with how it would have been coded in the 4th edition. The Heme Manual and Database currently are based on the 4th edition. Physicians are using the 5th edition blue book, whereas the cancer registry field is not yet at this time.

Regarding the Heme Manual and Database, this type of scenario is not covered because it is part of the 5th edition WHO Blue Book. The database cannot be updated until the 5th edition is approved for implementation (2026).

Assign 8013/3 (combined large cell neuroendocrine carcinoma). There are two histologies present: large cell NEC and urothelial. Literature search found primary large cell NEC of the bladder is extremely rare with less than 20 reported cases. This case does not fall into the site-specific rules and given it's raity, a specific rule for this situation was not and will not be added to the Bladder rules. See #1, Example 2, in the general instructions for coding histology.

Assign histology code, 8077/2 (squamous intraepithelial neoplasia, high grade) for LIN III and for LIN II. ICD-O-3.2 lists squamous intraepithelial neoplasia, grade II and grade III as 8077/2 indicating it is reportable. ICD-O-3.2 does not list every site-specific type of intraepithelial neoplasia. Check the SEER manual for reportable and non-reportable examples.