VALENCIA, Calif. ( TheStreet) -- MannKind ( MNKD) founder and CEO Al Mann has assured investors that positive results from two phase III studies of his inhaled, fast-acting insulin Afrezza due in August will lead quickly to an FDA approval filing. But no one at MannKind, including Mann, talks at all about a third, ongoing phase III lung safety study of Afrezza. Strange. This 510-patient study, currently open and enrolling, is titled "Evaluate Safety of Technosphere Insulin Inhalation Powder on Diabetic Subjects With Mild Obstructive Pulmonary Disease." Technosphere Insulin Inhalation Powder is Afrezza. According to the ClinicalTrials.gov registry, MannKind last updated and verified this large Afrezza lung safety study in February with scheduled completion in 2015. Remember, MannKind is promising to re-file Afrezza with the FDA before the end of the year on the basis of two efficacy studies known as Affinity-1 and Affinity-2. But if FDA doesn't also want to review data from this separate and equally large lung-safety study set to complete in 2015, why is MannKind spending the money to run it? One possibility, of course, is that FDA wants more lung safety data on Afrezza. That's not surprising, given the poor tolerability and depressed lung function attributable to Afrezza in a previous, large safety study conducted by MannKind and reported first in 2009. Results from this safety study were included in MannKind's original approval application for Afrezza rejected twice by FDA already. The two-year study enrolled 2053 patients with Type 1 and Type 2 diabetes and compared changes in lung function between Afrezza or usual diabetic therapy (Usual Care.) MannKind announced results of this Afrezza lung safety study in 2008 and data were presented at a European diabetes conference in 2009. The study was also published in the journal Diabetes, Obesity and Metabolism in February 2012. MannKind has long claimed the safety study showed no difference in adverse events or lung function between Afrezza-treated patients and those on usual care. The actual data from the study tell a different story. The drop-out rate for Afrezza patients was 49.4% compared to 30.4% in the usual car arm. Cough was the leading cause of discontinuation for Afrezza patients and was reported as an adverse event by 28% of Afrezza patients overall. Only 4% of patients treated with usual care reported cough as an adverse event.