I am so sorry to read about your sister's diagnosis. Sadly, I know what it feels like to have a sister diagnosed with cancer.
You're right, Cancer is cancer. Leading a healthier lifestyle from here on out can only help her, but it's highly unlikely it was her lifestyle that caused the cancer.
A little bit of my history, because I feel the need to throw a very large bucket of cold water on what I see as a HORRIBLE misrepresentation on your thread.
On May 5, 2008, my beloved little sis was diagnosed with brain cancer. Further biopsy showed that it's a very rare and aggressive glio neuroma brain tumor. It's most closely related to Glioblastoma Multiforme, which is the most aggressive brain cancer that there is.
DH had a tumor in his frontal lobe in his 20s. He refused western medical care (and had to hire an attorney to keep the diagnosing doctors off his case when they were threatening him with being committed and having care despite his wishes). This tumor was not malignant, but it was growing so fast "they" gave him 6 months to live without their treatment. He refused b/c they said surgery wasn't possible, and it was only radiation being shot at the frontal lobe...the side effects that were possible, he felt, were worse than death.
All primary brain tumors are considered malignant, regardless of how fast they are growing. They are graded on how fast they are growing. If his tumor was growing fast it was not only malignant, but it was a high grade malignancy. (Glioblastoma Multiforme is one of the few tumors that is known to have a bleak survival rate such as 6 months)
Also, brain tumors generally come back. I've only heard of cases in children where tumors stayed gone once they were gone. Adults can have many years before the tumor comes back, but it almost always comes back and it's usually much worse when it comes back. Your husband may want to continue to monitor his head via MRI to make sure that his tumor isn't slowly growing back, despite his diet.
I am wondering what were the biopsy results for his tumor. ie what kind of tumor did he have? Doctors will not suggest any course of treatment before biopsy, and since they knew that they couldn't operate and radiation was the only answer, then they must have biopsied and known what they were dealing with. I'm interested because I'd like to know if his cancer was similar to my sisters.
He went on a beyond-macrobiotic diet, where he coudln't even have fish (usually a part of macro) b/c the fish readily available in the States are so toxin-filled, he juiced, he did supplements, he did hyperbaric chamber treatments. He paid out of pocket for it all b/c they aren't covered by insurance even now, and it was crazy-hard (he had to move back in with his mom) b/c he was making under 30K at the time while in the Seattle area.
I have asked this of someone once before, but would you PLEASE share specific details of this diet cure-all for cancer? If you or your husband had the cure to cancer, you'd not only be rich and famous, but the entire medical industry would be on its ear . Can you imagine the validation for finally proving that diet has more power than doctors and medicines? It'd be a huge victory for the holistic approach to medicine.
To me, personally, it'd be a favor. My sister is no longer tolerating her treatments, and has to back off from almost everything that she's done medically to shrink her tumor. She can possibly do radiation again, but it's risky. Surgery is very risky as it'll likely paralyze her on her entire left side. Avastin is causing negative side effects, and Temodar is no longer tolerated by her (or is working) at all. Frankly her prospects for living many more years aren't good, and you could save a life other than your husbands if you share specific information about how he cured his brain tumor.
He also paid for MRIs throughout, also paid for OOP, and within 6 months it was responding. Within a year, I believe, it was gone.
Would you please share scans of those MRIs proving that your husband, you believe, cured cancer with his DIET alone? I have seen way too many MRI photos of cancerous brain tumors (remember, they're
all cancerous) and I'd love to see some good news for once.
Diet CAN have affects even on scary "cells growing and not stopping and creating tumors" problems.
I believe that diet can help the situation. I think it's medically irresponsible for anyone to tell the world that diet alone can cure cancer unless there is proof.
Unless you are willing to share proof, or share your cure with the world, I don't think you should blindly tell the world that diet cures cancer. I sincerely hope that nobody on a message board would believe what you are saying without more proof as well.
OP, I am so sorry to take your thread off topic. I really do feel badly for you, your sister, and your entire family. This diagnosis really turns a family upside down, and the last things you need are bad medical advice or more turmoil.
And that this is easy to treat and no big deal. 
Who know? We can play tricks on our minds whenwe don't want to face something. Or maybe she understands that thyroid cancer is highly treatable, so she's just not all that worried. I agree that cleaning up a bad diet, getting more active, getting adequate rest, et al, will make anyone feel better. But sometimes telling someone that, especially if they are facing a serious or chronic illness, can *feel* like criticism. 
