Hmmm... I haven't run across the potential connection between possible lung cancer and insulin in the type 1 pneumocytes, where it would predominate (see alveolus image above, "squamous alveolar cell"). t1 pneumocytes do pretty much nothing more than provide the thin, permeable barrier between the capillary blood flow and the inhaled air. They have a very flattened, fried-egg-like shape, with a very large surface area of the two flattened, basically touching thin membranes, and the nucleus and all the organelles of the cell bunched up in a compact knot. Molecules diffuse across this double membrane -- abeit much thinner than typical human ce membranes. Pneumocytes are specialized cells, of course :-)
The air-side surface of the t1 pneumocytes it coated with a thin layer of wet mucus that acts like a filter / fly paper to protect the delicate cell membrane underneath. This mucus is secreted by type 2 pneumocytes (Great alveolar cell in illustration).
With Afrezza, the particles are minute compared to the alveolus -- 2 million would fit in the typical alveolus. Keep that proportion in your mind as you imagine a particle contacting the mucus coating, which it must get through to get to the cell membrane of the t1 pneumocyte.
Upon contacting the water in the mucus, it dissolves. The insulin and the FDKP dissociate. I don't yet know what happens to the FDKP.
The insulin, at this point, is still not in contact with any tissue. It can not have any effect -- beneficial or harmful -- until it passes into the blood, or the interior (cytoplasm) of cells in direct contact with the insulin.
So, at this point we need to understand what happens, overall, to all the insulin. Obviously, some large portion diffuses through the t1 pneumocytes encapsulating the alveolus into the bloodstream. Also, though, as you have noted, some significant portion is still present in the mucus many hours after inhalation (30% @ 4rs in your cite).
The question I have is: How physiologically significant is this insulin if it's suspended in the mucus? Mucus is much thicker than blood, so I'm unclear on how insulin would act with IGF-1 receptors (insulin-like growth factor).
All I'm saying here (and it sounds real smart, but really, I'm learning a lot of this as I go), you and your doctor have raised a good point, one I'd like to understand the mitigating arguent to... more research!
In the mean time, I see some big differences in the whole environment in the lungs compared to other tissues vis a vis anything entering from the air side of alveoli, so there may be good reasons the pulmonologists gave the green light.
As always, anything I find I'll share!