If you are planning on trying to conceal a condition, or have selective memory about your medical history, think about this.
You join the Navy to see the world. They send you to Afghanistan, Lybia, Iraq, Djibouti, etc. You get a cold, you have a severe asthma flare, you're F'd and so are your troops. What happened to my synthroid???! Oh crap! Yeah, just go to the pharmacy. Being in the military is no joke. Being deployed and responsible for the health of your troops is no walk in the park. Astrocytoma? You're delusional to even ask. Maybe if surgery was 10 years ago.
If you develop problems after you're in, that's a different story.
And, if they find out about your fraudulent enlistment, you are seriously, seriously f'd. Enjoy explaining your dishonorable separation to the civilian employers.
One of my old colleagues was not deployable due to severe asthma, supposedly worse after she had a baby? Sure, why not. Too bad for her partners that had to deploy in her place. Fair? I would have boarded her out. She's a liability to the department. Worst of all, she wanted to be career navy. 20 years of dodging deployments and screwing over her peers. She was no rocket scientist either. Don't be that girl.
The military is not for everyone.