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SEER Inquiry System - Report
Produced: 12/24/2025 5:34 PM
Question 20230027
Inquiry Details
References:
#1: WHO Class CNS Tumors, 275-278. 5th edition
#2: Solid Tumor Rules. Malignant CNS and Peripheral Nerves, March 2023 Update
Question:
Solid Tumor Rules/Multiple Primaries--Peripheral Nerves: How many primaries should be abstracted, and which M Rule applies, when a malignant peripheral nerve sheath tumor (MPNST) in the right arm (C471) is followed greater than one year later by a separate malignant peripheral nerve sheath tumor of the thoracic chest wall (C473)? See Discussion.
Discussion:
Since the peripheral nerves are included in the Malignant CNS schema of the Solid Tumor Rules, neither the differences in subsite nor timing indicate these are separate primaries (Rule M10 indicates a single primary). However, these are separate MPNSTs in different sites and the tumors are not stated to be metastasis. Additionally, these are treated as separate primaries by the managing physician.
While the malignant CNS tumors do not take timing into account, is this correct for these peripheral nerve tumors that are often treated similarly to soft tissue tumors? Should Rule M8 be updated to include tumors in different peripheral nerve subsites?
Answer:
Abstract a single primary using Solid Tumor Rules, Malignant CNS and Peripheral Nerves, Rule M10 based on the information provided. Rule M10 applies as both non-contiguous tumors are of the same histology; i.e., on the same row in Table 3. As MPNST can arise in many sites, look for information about the precise location and tissue type in which the tumor arose. For example, if the tumors are stated to arise in soft tissue, follow the Multiple Primary Rules for Other Sites.
Both WHO Classification of Central Nervous System Tumors and WHO Classification of Soft Tissue and Bone Tumors state that MPNST is a malignant spindle cell tumor often arising from a peripheral nerve, from a pre-existing benign nerve sheath tumor, or in a patient with neurofibromatosis type 1 (NF1).
Future updates will move C470-C479 from CNS to other sites module.
