The incidence of lung cancer is greater among patients with idiopathic pulmonary fibrosis (IPF), compared with the general population, and is associated with a worse prognosis, a new U.S. study reports.
The study, “Characteristics of lung cancer among patients with idiopathic pulmonary fibrosis and interstitial lung disease – analysis of institutional and population data,” was published in the journal Respiratory Research.
Although it is known that an association exists between IPF and lung cancer, previous studies from the United Kingdom and Japan showed widely varying estimates of the prevalence of lung cancer among these patients.
Interstitial lung disease (ILD) is a term that broadly describes a diverse collection of many different lung disorders that affect the tissue and space around the alveoli (air sacs), called the interstitium. One form of ILD of unknown cause is IPF.
The study, led by researchers at the University of Pittsburgh, compared the incidence of lung cancer in patients with either IPF or ILD of a different cause (non-IPF ILD) with that in the general population. The study was based on data from the Simmons Center for Interstitial Lung Disease collected from 2000 and 2015.
The team analyzed data from 1,953 patients, including 1,108 IPF patients and 841 patients with non-IPF ILD. Of these, 31 IPF patients (2.8%) and 16 non-IPF ILD patients (1.9%) developed lung cancer. This difference was not statistically significant, the researchers noted.
Results also showed that IPF patients exhibited a 3.34-fold higher incidence of lung cancer, compared to the general population. In patients with non-IPF ILD this incidence was 2.3-fold higher.
The team also investigated the characteristics of lung cancer arising among IPF and non-IPF ILD groups, and also in the general population. The questions: Were they different? If so, how?
They found that “lung cancer in IPF is phenotypically distinctive from ‘sporadic’ lung cancer.” “Phenotypically distinctive” means that certain cancer characteristics in IPF patients differ from lung cancer in the general population. For instance, in IPF patients, lung cancer preferentially affected the lower lobes (63% of the cases compared to 26% in non-IPF patients), and frequently was of the type squamous cell carcinoma (41% versus 29% in non-IPF).
Interestingly, the team found that “fewer IPF patients with lung cancer were former or current smokers compared to lung cancer patients without IPF (77 vs. 90%),” they wrote, which supports the idea “that IPF is a risk factor for lung cancer independently of smoking.”
Regarding mortality, researchers found that lung cancer worsened the mortality rate among IPF patients compared to the non-IPF ILD group (84 versus 63% over the 15-year period analyzed).
Based on the results, the team concluded: “Lung cancer is approximately 3.34 times more frequently diagnosed in IPF patients compared to general population, and associated with worse prognosis compared with IPF without lung cancer, with squamous cell carcinoma and lower lobe predilection.”
According to the researchers, further studies are needed to better understand how lung cancer affects IPF patients, “and if screening for lung cancer in this population will ultimately impact the course of the disease,” they wrote.