I went to Baltimore today to get genetic test results from my doctors at Johns Hopkins. The results were somewhat inconclusive. It seems that my case is unusual even among unusual cases of cancer.
The first test was for microsatellite instability. They examined the DNA of my cancer cells to check for excessive repeats in the base sequences. Two of the five markers they examined were unstable, qualifying the specimen as having high microsatellite instability (MSI-H). That result is suggestive of a hereditary factor. It's also correlated with a better prognosis: "Colorectal carcinomas with no indication of microsatellite instability (MSS) have been associated with worse stage-specific survival after surgical and adjuvant therapies than those with MSI-H."
The second test looked at the expression of protein production in the cancer cells. With high microsatellite instability they expect certain proteins to be missing from those cells. However, my results showed that all of the proteins they checked were present. It's possible that the proteins were present but nonfunctional due to mutations or misfolding.
Since these first two tests suggest a hereditary cause but are inconclusive themselves, the next step is to examine certain genes from my normal tissue. There are four genes known to be involved in hereditary colorectal cancers and defects in two of those genes produce 90% of the cases. So they will start by checking those first two genes.
I'm not sure whether being diagnosed with hereditary colorectal cancer would be good news or bad. The average prognosis is better, but it also means a greater chance of recurrence and a greater risk for my relatives. The information is also interesting to the doctors at Johns Hopkins academically and might help direct treatment some day in the future.