ICD-10 Code C78.1 – Secondary malignant neoplasm of mediastinum (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C78.1 – Secondary malignant neoplasm of mediastinum
What it is
This code identifies metastatic cancer that has spread to the mediastinum, the central chest area between the lungs. Use it when the record clearly states a secondary malignant neoplasm in this site.
Clinical signs
Clinical features vary; refer to documentation. Patients may have findings related to a mediastinal mass, such as chest discomfort, cough, shortness of breath, or imaging evidence of metastatic disease.
When to use this code
Use C78.1 when the provider documents secondary malignant neoplasm of the mediastinum or metastatic involvement of that anatomic site. It is appropriate when the mediastinum is the confirmed metastatic location, even if the primary cancer is elsewhere. Check documentation if the note only says “metastatic cancer” without a site.
Do not use for
Do not use this code for a primary mediastinal tumor or for nonspecific chest malignancy without confirmed metastatic involvement. If the record does not specify secondary disease, check documentation.
Coding tip
Code the primary malignancy first when documented, and use C78.1 only for confirmed mediastinal metastasis.