Solid Tumor Rules

Solid Tumor Rules. Malignant CNS Site-group instructions and non-Malignant CNS Site-group instructions

There are two sets of Solid Tumor Rules for CNS: Malignant and non-Malignant.

A key difference in the Solid Tumor Rules for CNS tumors is the presence of specific guidelines for cases in which a benign or borderline tumor is followed by a malignant tumor. In these situations, the tumors are not always considered a separate primary.

• If a patient is diagnosed with a benign/borderline tumor, has surgical treatment, and then later is diagnosed with a malignant tumor, this is two primaries; however, if the patient only has Active Surveillance, the tumor may be the same primary. The Solid Tumor Rules provide detailed instructions on this.

Multiple tumors may be the same primary or different primaries. The type of histologies involved will make the determination.

Updated: September 23, 2026