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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.

Rule H4 states: Code 8723/3 (malignant melanoma, regressing) when the diagnosis is regressing melanoma. However, if the diagnosis was strictly regressing melanoma or malignant melanoma, regressing, the first rule that applies is Rule H1 because regressing melanoma is a single, specific histologic type and Rule H1 states: Code the histology when only one histologic type is identified. Following the current rules, one would never arrive at Rule H4. Should the H Rules be reordered? Or should an example of when one would use Rule H4 be added to clarify when to use this rule?

Rule H6 states: Code 8742/3 (Lentigo maligna melanoma) when the diagnosis is lentigo maligna melanoma with no other histologic types. However, if the diagnosis was strictly lentigo maligna or lentigo maligna melanoma, the first rule that applies is Rule H1 because lentigo maligna melanoma is a single, specific histologic type and Rule H1 states, Code the histology when only one histologic type is identified. Following the current rules, one would never arrive at Rule H6. Should the H Rules be reordered? Or should an example of when one would use Rule H6 be added to clarify when to use this rule?

Rule H8 of the Melanoma Solid Tumor Rules states that multiple variants of melanoma in one tumor are rare and a question must be submitted to Ask a SEER Registrar (AASR) for the correct histology code. However, our facility has seen a number of these cases in 2021 and would like to track the official answer and make it available to all in this format.

How should histology be coded for the following?

1. January 2021 diagnosis of left shoulder invasive malignant melanoma, histologic type: nodular and desmoplastic types per College of American Pathologists (CAP) summary of punch biopsy.

2. May 2021 shave biopsy of left arm invasive malignant melanoma, superficial spreading and nodular variant is listed in the CAP summary.

3. June 2021 diagnosis of right cheek invasive malignant melanoma, histologic subtype: superficial spreading and nodular seen on CAP summary of shave biopsy.

Rule M11 states: Abstract a single primary when there are urothelial carcinomas in multiple urinary organs, but neither the Rule nor the Notes describe the timing of these multiple urinary organ carcinomas. Timing requirements for other rules are clearly stated.

Does Rule M11 have a timing requirement or is it intended to apply to all urothelial carcinoma tumors regardless of timing (and not already qualifying for application of a previous M rule)?

Rule M15

Abstract a single primary when synchronous, separate/non-contiguous tumors are on the same row in Table 2 in the Equivalent Terms and Definitions.

Note: The same row means the tumors are

• The same histology (same four-digit ICD-O code) OR

• One is the preferred term (column 1) and the other is a synonym for the preferred term (column 2) OR

• A NOS (column 1/column 2) and the other is a subtype/variant of that NOS (column 3) OR

• A NOS histology in column 3 with an indented subtype/variant

Example: TURBT shows invasive papillary urothelial carcinoma 8130/3 and CIS/in situ urothelial carcinoma 8120/2. Abstract a single primary. Papillary urothelial carcinoma and urothelial carcinoma are on the same row in Table 3.

Rule M4 does not seem to apply because Note 1 defines clinically disease free to mean no evidence of recurrence in the same lung on follow-up. Patient had been disease free in the left lung after 09/2014 diagnosis. The 04/2019 diagnosis was in a different lung than the 4/2016 diagnosis.

The next applicable rule is either M11 or M14 depending on how we should compare the new 2019 tumor: to the most recent prior tumor in 2016 or to both prior tumors.

Rule M4 was added to the Other Sites M Rules to address diagnoses of small cell carcinoma following prostate adenocarcinoma, but Rule M4 states the diagnoses must be greater than one year apart.

In this situation, the diagnoses were less than one year apart and one must continue through the M Rules. The next M Rule that applies Rule M19: “Abstract multiple primaries when separate/non-contiguous tumors are on multiple rows in Table 2-21 in the Equivalent Terms and Definitions. Timing is irrelevant.” If one were to STOP at the first rule that applies, one would stop at Rule M19 which confirms the prostatic adenocarcinoma and small cell carcinoma are separate primaries, regardless of timing. If these are not to be accessioned as multiple primaries, does an Exception need to be added to M19?

Rule M6 clearly states that an invasive melanoma occurring more than 60 days after an in situ melanoma is a multiple primary. However M7 states that any melanomas diagnosed more than 60 days apart are multiple primaries. Since M7 does not state malignant melanomas diagnosed more than 60 days apart, this implies that any scenario:

in situ following an invasive,

invasive following an in situ,

in situ following an in situ,

or invasive following an invasive

are all multiple primaries if more than 60 days apart. If that is the intent of M7, then M6 is totally unnecessary. If the intent of M7 is only for an invasive following an invasive, then the word malignant needs to be inserted as the first word of rule M7.

Rule PH28 confirms the more specific histologies are ignored if this is truly a low grade B-cell lymphoma (i.e., non-Hodgkin lymphoma, NOS) since both MALT lymphoma and LPL are more specific types of low grade B-cell lymphomas. This leaves only a diagnosis of low grade B-cell lymphoma with plasmacytic differentiation to consider.

SINQ 20130033 states a low grade B-cell lymphoma with plasmacytic differentiation should be coded as 9680/3 (diffuse large B-cell lymphoma (DLBCL)). However, DLBCL is a high grade B-cell lymphoma, not a low grade B-cell lymphoma.

If the pathologist classifies this as a non-specific low grade B-cell lymphoma, and clarifies that this may represent a more specific type of low grade B-cell lymphoma (MALT lymphoma or LPL), should the histology be coded to a high-grade lymphoma (DLBCL) or non-Hodgkin lymphoma, NOS?