An official website of the United States government
Home
SEER Inquiry System - Report
Produced: 03/03/2026 2:41 PM
Question 20110073
Inquiry Details
References:
Subject matter expert
Question:
Discussion:
1/28/08 Patient was diagnosed with spindle cell sarcoma in the right gluteus muscle. Metastatic tumors were found in a vertebral body and in the lung. Chemotherapy was started.
4/22/08 PET scan done to evaluate response to chemo. The primary tumor had increased in size. New mass in the left thigh that was highly suspicious for metastasis found. (The left thigh tumor was not accessioned at that time as it was described as a metastatic tumor.)
7/3/09 Left thigh tumor was resected and path revealed spindle cell sarcoma. There was no mention that it represented metastasis.
Does the left thigh tumor represent a new primary per rule M12? Or does the previous clinical description of the left thigh tumor representing metastasis have priority?
Answer:
this is a single primary per Rule M1. According to our expert pathologist, "if multiple solid tissue tumors are present (sarcomas), then almost always there is one primary and the rest are metastases. There are infrequent occasions of multifocal liposarcoma or osteosarcoma occurring, but the patient would be treated as a patient with metastatic disease."
The steps used to arrive at this answer are:
Open the Multiple Primary and Histology Coding Rules manual. For a soft tissue primary, use one of the three formats (i.e., flowchart, matrix or text) under the Other Sites MP rules to determine the number of primaries because soft tissue primaries do not have site specific rules.
Go to the UNKNOWN IF SINGLE OR MULTIPLE TUMORS module, Rule M1.
Rule M1 states, "It is not possible to determine if there is a single tumor or multiple tumors, opt for a single tumor and abstract a single primary." Given the information from the expert pathologist, this case should be reported as a single primary applying this rule.
