ICD-10 Code C45.9 – Mesothelioma, unspecified (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C45.9 – Mesothelioma, unspecified
What it is
C45.9 identifies mesothelioma when the site is not specified in the record. Use it for a malignant tumor arising from mesothelial tissue when documentation does not name the pleura, peritoneum, or another location.
Clinical signs
Clinical features vary; refer to documentation. Commonly, mesothelioma is confirmed by pathology and may present with nonspecific findings such as effusion, chest or abdominal symptoms, or a mass.
When to use this code
Use this code when the provider documents mesothelioma but does not identify the anatomic site. It also fits cases where the record says “unspecified mesothelioma” or provides insufficient detail for a more specific code. Review pathology, imaging, and final diagnoses before coding.
Do not use for
Do not use C45.9 if the record clearly identifies pleural, peritoneal, pericardial, or other specific mesothelioma site. Also avoid it for benign mesothelial conditions or other malignancies; check documentation.
Coding tip
If the site is missing, code the unspecified diagnosis only after confirming no more specific location is documented anywhere in the chart.