Hairy cell leukemia is a chronic lymphotic leukemia (CLL), and the disposition of the FAA medical certificate comes down to individual diagnosis, which involves stage,

It is cited by the Aviation Medical Examiner's Guide: https://www.faa.gov/ame_guide/app_pr...ech/item45/amd

The disposition table (breakdown chart) which details how your particular stage of cancer may be handled is found at: https://www.faa.gov/ame_guide/media/...ispo_table.pdf

With Stage 0-2 and oncology of less than five years, the aviation medical examiner must defer to the FAA, for special issuance. This will require that you're asymptomatic (no symptoms), and treatment of the disease is by observation-only. It requires progress notes from a board-certified oncologist, within 90 days of submitting paperwork to the FAA and deferral of your FAA medical. It will need to include appropriate laboratory work (CBC, beta-2 microglobulin), flow cytometry, any treatment plan moving forward, and completion of the FAA's status sheet (https://www.faa.gov/ame_guide/media/...us_summary.pdf). As noted above, this is something you should step through via AMAS.

A note about AMAS: their job isn't treatment, but streamlining paperwork. They are not AME's, but have a special status with the FAA as advisors (sort of AME-advisors, if you will), and are all experienced flight surgeons who advise you on the necessary paperwork, collect it from you, and submit it to the FAA on your behalf, with their recommendations. They charge an initial consultation fee by email or phone (they'll be very brief), and then a fee for the case, which will typically be about twelve hundred dollars, paid up front (the specifics for your case will be up to them to detail to you). Some expect AMAS to be the secret sauce to get around the system; they don't do that. They process paperwork and advise, without any sugarcoating. They expedite by collecting the paperwork that you send them, making sure it's complete, and then submit it directly to the Federal Flight Surgeon as one packet. The chief advantage of working through them is that it cuts down on or eliminates numerous delays as the FAA asks for more documentation.

This is a process I wouldn't try to navigate on your own; the additional costs are worth the price of admission to ensure everything is done correctly initially, and going forward.

Yours is a rare condition, considered a chronic one, which may be a good candidate for special issuance and restoration of medical privileges. Before you proceed further, I'd contact AMAS for the initial consultation first, such that you can establish a game plan of exams, paperwork, and expectations, and a general timeline for accomplishing everything.

As with all things, your own health must come first, regardless of the FAA outcome.