In situ colorectal cancer rates

[Lindsey Hutchison]

I am working on a project using in situ colorectal cancer rates. The in situ rates for NYS are an order of magnitude higher versus SEER in situ rates. When I looked at in situ rates within SEER, some of the registry rates vary by an order of magnitude as well. Any insight on this would be appreciated. Thank you!

[Jim Hofferkamp]

A few reasons i can think of that may explain some of the differences.

1. Reporting from surgery centers. If a patient has a colonoscopy with polypectomy and is found to have a low grade in situ tumor, they may not receive any additional treatment. A more invasive tumor would probably be treated with resection. If the central registry doesn’t have good reporting from surgery centers, their in situ cases may be down.
2. High grade dysplasia is a big issue among pathologist. Some pathologist consider high grade dysplasia to be carcinoma in situ and others do not. Each facility is responsible for determining when or if a high grade dysplasia should be abstracted as carcinoma in situ. If some of the larger facilities are reporting some or all of their high grade dysplasia cases as carcinoma in situ, it could impact rates.
3. A less likely explanation might be the AJCC definition of Tis for colon. A Tis for colon includes tumors that invade the lamina propria. They do this because these patients should be treated like in situ cases (not like T1 patients). Even though the T value is Tis, these cases should have a behavior of /3 and summary stage of 1-localized. However, some registrars see that AJCC calls these Tis and assume the behavior should match.

[David O’Brien]

I have access to the NCR & SEER Incidence State RAD file for 1999-2013 via SEER*Stat. For the most recent 5 years of data (2009-2013), I see that the age-adjusted rates for in situ colorectal cancer range from a high of 4.0 per 100,000 in PA to a low of 0.4 in WA, an order of magnitude as you point out. The number of cases in WA is relatively small (111) compared to PA (2,582). Even though the population of PA is about twice that of WA, the number of cases in WA seems unusually low. My own state of AK is at 1.8, which is just below the national rate is 2.0. So it may very well be a reporting issue as Jim Hofferkamp suggests in his response to your question. And interesting thing to note is that the national rate has fallen by about half (4.1 to 1.9) from 1999 to 2013, and the number of cases have dropped significantly (10,445 to 6,908).

[Francis Boscoe]

Thank you Jim and David – I am helping Lindsey write up these results. It reminds me of the variations in lip cancer I looked at a few years ago. It’s almost like you could have a rule of thumb – wherever you have debate about what should count and what shouldn’t count, expect an order of magnitude variation in rates between registries.

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