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Rule H13 states to code the histology to metaplastic carcinoma when there is metaplastic carcinoma (or a subtype/variant) and invasive carcinoma NST. This rule makes no mention of lobular carcinoma. However, in Table 3, Note 2 for metaplastic carcinoma (8575) states metaplastic carcinoma, NOS and subtypes are almost always mixed with invasive mammary carcinoma, NST and at times lobular carcinoma. These tumors should be coded to metaplastic regardless of percent invasive mammary carcinoma or lobular carcinoma present.

While Table 2 (the mixed histology code table) does include an entry for metaplastic carcinoma AND carcinoma NST OR lobular carcinoma, it is unclear why lobular carcinoma has not been added to Rule H13 as well.

If a single tumor has metaplastic plus lobular carcinoma, Rule H13 does not apply and one has to continue through the rules. Unfortunately, the next rule registrars would be tempted to use is Rule H18: Code the histology that comprises greater than 50% of tumor when two histologies are on different rows in Table 3. This Rule does not state it does NOT apply to metaplastic carcinoma (only mucinous). So, if for some reason the lobular was greater than 50%, the incorrect histology would be coded (unless the registrar happened to remember Note 2 in the metaplastic carcinoma entry in Table 3).

This question was prompted from preparing SEER*Educate coding exercises. We will use the answer as a reference in the rationales.

Per the 2018 Solid Tumor Rules instructions, Final Diagnosis and Staging Summary (synoptic report) have equal coding priority. However, it is unclear which takes priority, or if this should be a combination of components, when the histologies are two different specific histologic types per Table 3 of the Breast Solid Tumor Rules Manual.

The 2018 Breast Solid Tumor Rules Equivalent Terms and Definitions - Changes from 2007 Multiple Primaries/Histology Rules states: Mammary carcinoma is a synonym for carcinoma no special type (NST)/duct carcinoma not otherwise specified (NOS) 8500. It will no longer be coded as carcinoma NOS 8010. Should metastatic carcinomas of breast origin be 8500, or is code 8010 (carcinoma NOS) more applicable because histology coding from metastatic sites is not as reliable?

In the April 2019 Breast Solid Tumor Rules update, the Priority Order for Using Documentation to Identify Histology was changed, giving equal priority to the Final diagnosis / synoptic report as required by CAP (item 2B).

There are technically two histologies documented for the case above; a Not Otherwise Stated (NOS)/No Special Type (NST) (invasive mammary carcinoma, per final diagnosis text) and subtype/variant (invasive cribriform carcinoma, per CAP report). If we do not use the synoptic report with priority over the final diagnosis, Rule H14 indicates the histology would be the NOS histology (invasive mammary carcinoma) because the percentage of tumor is not given for the subtype. However, SINQ 20180045 states, In the CAP protocol, the term Histologic Type is a label where the histology that corresponds to the largest carcinoma is collected. According to the CAP protocol for invasive breast cancer, the histologic type corresponds to the largest carcinoma.

If the pathologist summarizes the findings in a synoptic report, should the specific Histologic Type identified have priority?

Patient had a breast excision that proved a single tumor with no evidence of invasive carcinoma. The final diagnosis stated: Size (extent) of EPC DCIS: Spanning approximately 1.3 cm. The pathologist did not describe separate foci of DCIS; only one tumor comprised of both encapsulated papillary carcinoma and DCIS. The encapsulated papillary carcinoma was not described as invasive. The pathology noted: This case is best classified as EPC conventional DCIS. No conventional stromal invasion is identified. Solid Tumor Rule M2 confirms a single tumor is a single primary.

However, there does not appear to be an H Rule that instructs how to code histology. The Single Tumor: In Situ Only module, has only three H Rules and none of them apply to this case. The patient does not have Paget disease (H1), does not have a single histology (H2, there are multiple histologies present as DCIS and EPC are listed on different rows in Table 3) and does not have DCIS and LCIS (H3). How does one arrive at the correct histology for this case?

The Histology Coding Instructions give priority to the Final Diagnosis over the CAP protocol. However, when pathology reports are formatted using the CAP protocol, the presence of in situ carcinoma is generally only mentioned in the CAP protocol. Can the presence of in situ tumor mentioned only in the CAP protocol be used to apply rule H7 (Single Tumor: Invasive and In Situ Components Module)? Or are the rules in the Single Tumor: Invasive Only module used?

Example: Final diagnosis is invasive ductal carcinoma. CAP protocol mentions,

Left frontal mass biopsy diagnosis comment states: Given the synaptophysin and patchy CD34 staining of these cells, the possibility of ganglioglioma and pleomorphic xanthoastrocytoma is raised. Astroblastoma and ependymoma were considered given the perivascular pseudorosettes, however GFAP staining is quite limited against these tumors. Reticulin stain shows limited perivascular reticulin staining however. Nevertheless, the necrosis, mitotic activity and elevated mitotic activity would point to a malignant neoplasm. Given the neural and limited GFAP staining, a generic classification of neuroglial is provided.

This is the only available information. Further clarification or discussion with the physician or pathologist is not possible. Therefore, is this diagnosis of neuroglial tumor equivalent to that described in SINQ 20091037?

Table 3 (Specific Histologies, NOS, and Subtypes/Variants) lists Ewing sarcoma as a synonym for Peripheral primitive neuroectodermal tumor 9364. Presumably, this is to be used for the reportable malignant peripheral nerve tumors when diagnosed as pPNET or Ewing sarcoma. However, this patient has a type of central (or CNS) primitive neuroectodermal tumor (histology 9473). Table 3 does not list central primitive neuroectodermal tumor (PNET or CPNET) as a valid histology for CNS tumors.

While Table 3 does not list all the possible histologies for the CNS, it currently is not clear how one would arrive at the histology code for a CNS Ewing sarcoma family tumor with CIC alteration, as this is recognized as a new entity for primitive neuroectodermal tumors of the CNS (i.e., PNET, histology 9473) per multiple journal articles. Ewing sarcoma family tumors include both peripheral PNET and central PNET tumors, but to code this histology as a peripheral PNET (9364) in this case seems incorrect when the primary tumor is stated to be of central nervous system origin, not peripheral nervous system origin.

Pituitary blastoma was not added to Table 3 (Specific Histologies, NOS, and Subtypes/Variants) of the 2018 Malignant CNS and Peripheral Nerves Solid Tumor Rules as part of the December 2020 update. This is a new malignant CNS histology for 2021 and later. Not including this histology in Table 3 results in the registrars being required to check another source to correctly code this histology. If this histology cannot be used for cases diagnosed prior to 2021, should that diagnosis year clarification be included in the STR?

This question was prompted from preparing SEER*Educate coding exercises. We will use the answer as a reference in the rationales.

Example: Posterior fossa tumor resection final diagnosis was medulloblastoma, WHO Grade IV. The diagnosis comment notes the current tumor resection reveals large irregular reticulin-free nodules with streams of neoplastic cells in a fibrillary background in association with narrow reticulin-rich internodular strands of poorly differentiated neoplastic cells. Taken together, these findings are indicative of medulloblastoma with extensive nodularity. The diagnosis comment provided only one histology.

Per the 2018 Solid Tumor Manual, Malignant CNS, Priority Order for Using Documentation to Identify Histology instructions, an addendum or comment has priority over the final diagnosis. Although indicative is not listed on any ambiguous terminology list, is this an ambiguous diagnosis that must be ignored? Or does the diagnosis comment in this case provide a single, specific diagnosis of medulloblastoma with extensive nodularity?