Progressive massive fibrosis (PMF), the worst form of black lung disease, is rising among coal miners, but the reasons for this trend remain unclear, according to research presented at ATS 2019. The researchers speculated that the increase was due, in part, to miners breathing in more crystalline silica as a result of newer mining methods; however, analysis of lung tissue samples through 1996 did not show an increase in silicotic PMF. Researchers analyzed data from the National Coal Workers’ Autopsy Study (NCWAS). Of 7,200 NCWAS cases available, 4,690 had adequate lung tissue and evidence of pneumoconiosis and had been classified by NIOSH pathologists. Of these, 387 cases had previously been classified as PMF, however only 325 had material currently available for review. These 325 miners were born between 1885 and 1942. There were 141 coal-type PMF cases, 107 mixed-type, and 77 silicotic-type PMF. There were no statistically significant differences in the distribution of these cases by PMF type over time, either by frequency or proportion. "Our findings suggest that the shift in mining exposures driving the resurgence in rapidly progressive pneumoconiosis and PMF likely occurred more recently [than 1982]," researchers wrote.