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SEER Inquiry System - Report
Produced: 01/13/2025 6:57 AM
Question 20200071
Inquiry Details
References:
Solid Tumor Rules. Breast; December 2020 Update
Question:
Solid Tumor Rules (2018)/Histology--Breast: Rule H13 of the 2021 Breast Solid Tumor Rules (a new H Rule added in the December 2020 revision) indicates metaplastic carcinoma is coded when both metaplastic carcinoma and carcinoma No Special Type (NST) are present. Should Rule H13 also address lobular carcinoma so the histology for a single tumor with metaplastic carcinoma and lobular carcinoma is correctly coded to metaplastic carcinoma (8575)? See Discussion.
Discussion:
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.
Answer:
Lobular carcinoma was unintentionally excluded from M13. It will be added in the 2022 update. It is important registrars learn to use the tables and read the notes.
