Tony,
most SSDI or SSI claims for cancer are based on cancer fatigue. Your age may work against you though, The SS people don't like to pay out for people under 50. You should also be fully vested in the program. Make an appointment at your local SS office and bring copies of ALL of your medical records with you and a certified copy of your birth certificate. They will want scan reports, lab tests, diagnosis, etc. In California anyway, they have a panel of state doctors look it over and approve the claim. If your claim is approved then there is a 6 month waiting period (which is retroactive to the date of disability) and they start to pay on the 7th month.

Here is a link to the SS disability page - be very careful to provide EXACTLY what they are asking for http://www.ssa.gov/d&s1.htm

I did my own claim and it was approved in 2 weeks. I was 55 at the time. I am still collecting full benefits 4 years later and they will run out next year. I did a 9 month, full time "trial back to work" period (during which you can make as much money as you can with no penalties). They allow for an additional 36 months of benefits after that, conditional on your income. If you are self employed they only consider your net. If you work and get a W2 then they consider your gross. After 2 years you are automatically eligible for Medicare as well. Being in regulatory affairs and working with government agencies for many years helped a lot also.

It sounds to me like your eligibilty date (based on when you started Tx 9/06) was in March 07 so you should get a retroactive check for 4-5 months if they approve your claim.

You may need a lawyer but really it's a fairly straight forward process if you comply meticulously with the documentation requirements and have enough paid into the system.