What is the role of sputum cytologic studies in the workup of non–small cell lung cancer (NSCLC)?

Updated: Jul 15, 2021
  • Author: Winston W Tan, MD, FACP; Chief Editor: Nagla Abdel Karim, MD, PhD  more...
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Answer

Centrally located endobronchial tumors may exfoliate malignant cells into sputum. (This location and tendency to exfoliate are most common in squamous cell carcinomas [SCCs].) Therefore, sputum cytology can be a quick and inexpensive diagnostic test if results are positive. The false-positive rate for sputum cytology is 1%, but the false-negative rate is as high as 40%.

Sputum cytology does not provide reliable distinction between different histologic subtypes. Discordant results are often observed between cytologic and histologic findings of specimens obtained from bronchoscopy or transthoracic biopsy.

The diagnostic accuracy of sputum cytology depends on rigorous specimen sampling (at least 3 specimens) and preservation techniques, as well as on the location (central vs peripheral) and size of the tumor. [51] The test detects 71% of central tumors but less than 50% of peripheral tumors; therefore, further testing must always follow a negative result.

Several large studies have not revealed that screening with sputum cytology and chest radiography is cost-effective in early detection. In one small study, a cytologic specimen was used to measure EGFR and KRAS mutations; however, this practice still needs to be validated. [52]

Sputum cytology is suggested for high-risk patients in whom semi-invasive procedures such as bronchoscopy or transthoracic needle aspiration (see below) might pose a higher risk. Currently, however, with the development of advanced x-ray imaging techniques and biopsy procedures, sputum cytology is not commonly employed in the diagnosis of NSCLC.


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