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SEER Inquiry System - Report
Produced: 03/04/2026 3:53 PM
Question 20240006
Inquiry Details
References:
#1: WHO Class Hem & Lymph Tumors. 4th edition
#2: Subject matter expert
Question:
Primary Site/Histology--Heme & Lymphoid Neoplasms: What are the correct primary site and histology for patient diagnosed with an oropharyngeal soft tissue mass revealing plasma cell neoplasm with 5-10% of marrow cellularity in 2022? See Discussion.
Discussion:
Patient underwent excision of an oropharyngeal soft tissue mass revealing plasma cell neoplasm with extensive amyloid deposition. During work-up, bone marrow biopsy also revealed involvement by plasma cell neoplasm, with 5-10% of marrow cellularity. No amyloid seen in bone marrow. Patient was referred for radiation of the oropharyngeal mass. Per medical oncology qualifying best for the diagnosis of solitary extramedullary plasmacytoma with minimal marrow involvement. Decision made for observation by medical oncology in view of “minimal” bone marrow involvement. Question: Is rule M11 correct, and I abstract this case as a plasma cell myeloma, 9732/3, C421?
Answer:
Code as an oropharyngeal primary site and histology as solitary plasmacytoma (9734/3) based on consultation with our hematological expert.
The WHO Classification of Hematopoietic and Lymphoid Tissues defines multiple myeloma as "bone marrow plasma cell percentage >60%." There are several other factors, but the bone marrow involvement is the key point for your case. The pathologist also states that the bone marrow is consistent with "plasma cell neoplasm," which by itself is not the same as multiple myeloma.
This case has 5-10% involvement by plasma cell neoplasm. This does not meet the bone marrow qualifications for multiple myeloma and is consistent with the pathologist's statement that there is minimal bone marrow involvement.
We will be updating the Hematopoietic and Lymphoid Neoplasms Database and Manual to clarify this (2025 updates).
