In determining multiple primaries, separate rules are used for non-malignant and malignant brain tumors. Rules are based on the specific data elements.

Timing (assuming same site and same histology)

• Malignant: 2 months
• Non-malignant: no limitation

The current timing rule for determining multiple primary tumors applies to malignant CNS tumors only. If two or more primary malignant intracranial or CNS tumors are diagnosed in the same site within two months of the diagnosis of the first primary, the tumors are counted as one primary. If multiple tumors of the same site are diagnosed more than two months apart, the tumors are counted as separate primary sites.

The current 2 month rule does not apply to non-malignant CNS tumors. Non-malignant tumors may recur in the same location. If they recur, even after 20 years, they are still the same tumor.

Site

• Malignant: 3 character level
• Non-malignant: 4 character level

For non-malignant CNS tumors, sites are different when there is a difference in the 4th digit of the site code, but the first 3 digits are the same. For example, spinal meninges (C70.1) and cerebral meninges (C70.0) are considered different primaries. (The exception is when the difference in the 4th digit occurs because the 4th digit of one site code is 9, which indicates a non-specific code.)

Malignant tumors remain as they are currently defined with differences only at the 3 digit level. Therefore, separate malignant tumors occurring in the cerebral meninges and in the spinal meninges (both C70) are not considered different primaries.

Laterality

Laterality should be coded for both non-malignant and malignant brain
tumors. Further, laterality is to be considered when determining multiple primaries for non-malignant tumors but not for malignant brain tumors.

CNS sites to be coded with laterality:

• Cerebral meninges, NOS (C70.0)
• Cerebrum (C71.0)
• Frontal lobe (C71.1)
• Temporal lobe (C71.2)
• Parietal lobe (C71.3)
• Occipital lobe (C71.4)
• Olfactory nerve (C72.2)
• Optic nerve (C72.3)
• Acoustic nerve (C72.4)
• Cranial nerve, NOS (C72.5)

Code laterality using codes 1 through 4 or 9 (paired site but lateral origin unknown; midline tumor). The laterality for all other CNS sites is coded 0 (not a paired organ).

Histology

• Malignant: 3 digit level
• Non-malignant: Histology Groups Table

The histology rules for counting multiple primaries have to be modified to count tumors at a level other than the first three digits of the morphology code.

The evolution and grading of brain tumors is such that a tumor may recur at a higher grade which has a different ICD-O-3 code number. In such cases, the new tumor is not counted as a new primary (except if it progresses or transforms from benign or borderline to malignant). The various four-digit histologies within each of these histologic groups will be counted as one primary. Thus the patient could have one glioma and one ependymoma, but not a low grade astrocytoma followed by a glioblastoma multiforme at the same site.

For counting non-malignant primaries, each of the following groups is considered ONE primary.

Histologic groupings to determine same histology for non-malignant brain tumors

Please use the two reference tables below to count malignant and non-malignant primaries.

B = Benign
M = Malignant