C39.9Malignant neoplasm of lower respiratory tract, part unspecified

C39.9 is the ICD-10-CM diagnosis code for malignant neoplasm of lower respiratory tract, part unspecified. It belongs to category C39 (malignant neoplasm of other and ill-defined sites in the respiratory system and intrathoracic organs), block C30-C39 (malignant neoplasms of respiratory and intrathoracic organs) and chapter 2 (neoplasms). It is billable, so it can be reported on its own for dates of service from October 1, 2026 through September 30, 2027.

Within C39, choose C39.9 (lower respiratory tract, part unspecified) only when documentation doesn't support a more specific option: upper respiratory tract, part unspecified (C39.0).

Use an additional code to identify: exposure to environmental tobacco smoke (Z77.22), exposure to tobacco smoke in the perinatal period (P96.81), history of tobacco dependence (Z87.891), occupational exposure to environmental tobacco smoke (Z57.31), tobacco dependence (F17.-) and 1 more.

It is not a CC or MCC, so as a secondary diagnosis it doesn't change the MS-DRG severity level.

In MS-DRG v44.0, it is part of the grouping logic for DRG 180 (Respiratory Neoplasms with MCC, relative weight 1.7806), DRG 181 (Respiratory Neoplasms with CC, relative weight 1.0936) and DRG 182 (Respiratory Neoplasms without CC/MCC, relative weight 0.7439), in MDC 04 (Diseases and Disorders of the Respiratory System), as a principal or secondary diagnosis. The DRG a claim lands in depends on the principal diagnosis, procedures and any CC/MCC secondary diagnoses.

It has been part of ICD-10-CM since the code set took effect on October 1, 2015 and hasn't changed since.

Before ICD-10, this condition was coded in ICD-9-CM as 165.8 (malignant neoplasm of other sites within the respiratory system and intrathoracic organs) and 165.9 (malignant neoplasm of ill-defined sites within the respiratory system).