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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.

In 2021, the patient was diagnosed with a non-reportable appendiceal LAMN.  Resection showed a tumor diffusely involving the appendix and perforating the visceral peritoneum, as well as extensive intraperitoneal metastasis.  In 2023, a lung wedge resection revealed metastatic mucinous neoplasm involving lung parenchyma and pleura, consistent with metastasis of the known appendiceal primary.  It is understood that intraperitoneal spread of an appendiceal LAMN does not make it reportable because the peritoneal disease is also non-invasive.  Does extraperitoneal metastasis of an appendiceal LAMN diagnosed prior to 2022 make it invasive disease and therefore reportable? 

Is Rule H8 a duplicate of Rule H7? Rule H7 instructs one to use Table 2 when there are multiple histologies and the combination is listed in Table 2 (or a combination code was received from Ask a SEER Registrar). Rule H8 states to code adenocarcinoma with mixed subtypes (8255) when there are multiple adenocarcinoma subtypes OR any combination of histologies which are not listed in Table 2. However, both conditions for Rule H8 are already included in Table 2 (the last row). How would one ever move past Rule H7 if all the conditions for both Rules H7 and H8 are covered first under Rule H7?

Example: A resection pathology report proves invasive adenocarcinoma, acinar, solid and papillary types. Rule H7 seems to be the first H Rule that applies as there are multiple histologies (identified using a reportable term: type) AND the combination is listed in Table 2. The last row of Table 2 instructs one to code Adenocarcinoma with mixed subtypes (8255) when there are at least two of the subtypes/variants of adenocarcinoma listed in Column 1 (Required Terms). In this case, there were three subtypes/variants that are listed in Column 1 (acinar, solid and papillary). However, Rule H8 also instructs one to, Which rule applies here, Rule H7 or Rule H8?

According to the ICD-O-3, the histology for IPMN adenoma is 8453/0 is non-reportable. However, per SINQ 20021099, this is reportable.

Pathology shows: Right liver lobe, partial hepatectomy " intraductal papillary neoplasm with high grade dysplasia.