ICD-10 Code C78.3 – Secondary malignant neoplasm of other and unspecified respiratory organs (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C78.3 – Secondary malignant neoplasm of other and unspecified respiratory organs
What it is
C78.3 identifies metastatic cancer involving respiratory organs not otherwise specified in ICD-10-CM. Use it when a malignant tumor has spread to an airway or lung-related site and the documentation does not name a more specific secondary site.
Clinical signs
Clinical features vary; refer to documentation. Commonly, records describe evidence of metastatic disease on imaging, pathology, or operative findings, with respiratory involvement such as cough, dyspnea, hemoptysis, or chest discomfort.
When to use this code
Use C78.3 when the provider documents secondary malignant neoplasm in an unspecified respiratory organ or in another respiratory site not captured by a more specific code. It also applies when the chart confirms metastatic spread to the respiratory system, but the exact organ is not named.
Code the primary malignancy separately when documented, and follow sequencing rules in the record. Check documentation if the site is unclear or if the lesion is only suspected rather than confirmed.
Do not use for
Do not use this code for primary lung cancer or for metastatic disease to non-respiratory organs. If the documentation specifies pleura, bone, liver, or another exact secondary site, choose the more precise code.
Coding tip
Look for the word “secondary” and confirm the respiratory site; unspecified wording supports C78.3 only when no more specific metastatic site is documented.