Solid Tumor Rules

Cancers from many primary sites metastasize to the lung. It is important to rule out metastases from another organ/site before abstracting a lung primary.

For lung cancers multiple primary determination focuses on several different factors.

• Neuroendocrine tumor/carcinoma and another non-small cell carcinoma
• Separate/non-contiguous tumors with different subtypes/variants
• Simultaneous multiple tumors
• Tumors in both lungs

The Lung Solid Tumor Rules should also be used to assign histology for lung primaries. Some tumors may have more than one histology present, and the rules will direct you to the appropriate histology code.

Per the Solid Tumor Rules for Lung

• Code the histology described as differentiation or features/features of ONLY when there is a specific ICD-O code for the “NOS with ____ features” or “NOS with ____ differentiation”.
• Note: Do not code differentiation or features when there is no specific ICD-O code

Solid Tumor Rules. Lung Rules

Updated: April 8, 2026