Colorectal and Urological Cancers May be Markers for Each Other

By Michael Smith
CHICAGO, 14 may 2008-- Colorectal cancer increases the risk for subsequent urologic malignancies, and vice versa, researchers here said.
The increase in risk in either direction was particularly noticeable when the first diagnosis occurred before the age of 60, reported David Rubin, M.D., of the University of Chicago Medical Center, and colleagues in the May issue of Archives of Internal Medicine.
The finding, derived from a retrospective database analysis, suggests that either diagnosis should be an alert to watch for tumors of the other type, Dr. Rubin and colleagues wrote.
The connection between urological and colorectal cancer has been seen previously in some specific groups -- such as those with hereditary nonpolyposis colorectal cancer -- but this study is the first to show the association in a large general population, the researchers said.
Using the Surveillance Epidemiology and End Results (SEER) public database, the researchers looked at 186,972 patients with urological cancers and 357,597 with colorectal disease, all diagnosed between 1973 and 2000.
Among those with urological disease, 52,449 had renal parenchymal cancer, 6,403 had renal pelvis cancer, 3,744 had ureteral cancer, and 124,376 had bladder cancer.
The colorectal patients included 251,946 with colon cancer and 105,651 with rectal cancer. In the report, data for the two categories were combined because results for separate analyses were similar.
Dr. Rubin and colleagues calculated standard incidence ratios (SIRs) of observed to expected cases of invasive colorectal cancer for each urologic cancer site and vice versa.
The analysis showed:
Patients with previous ureteral cancer had an 80% increase in the risk of subsequent colorectal cancer, with an incidence ratio of 1.80 and a 95% confidence interval from 1.46 to 2.20.
Those with renal pelvis cancer had a 44% increase in the risk of colorectal disease, with an incidence ratio of 1.44 and a 95% confidence interval from 1.20 to 1.72.
Patients with bladder or renal parenchymal cancer had small but statistically significant increases in the risk of subsequent colorectal cancer, but the researchers concluded the increases were probably not clinically significant.
The risk for any urologic cancer was increased after a diagnosis of colorectal cancer, with an incidence ratio of 1.24 and a 95% confidence interval from 1.20 to 1.28.
The researchers found that the highest risk increase for subsequent colorectal cancer was among those who received the diagnosis of renal pelvis or ureteral cancer before 60.
The incidence ratios were 4.94 and 3.16, respectively, for those diagnosed before the age of 50 and 2.74 and 2.20 for those diagnosed between 50 and 60.
On the other hand, the highest risk for subsequent renal pelvis and ureteral cancers was seen in patients with a colorectal cancer diagnosis before the age of 60
The incidence ratios were 6.20 and 6.37, respectively, for those diagnosed before the age of 50 and 2.32 and 4.81 for those diagnosed between 50 and 60.
Dr. Rubin and colleagues also found that patients diagnosed with multiple primary colorectal cancers had incidence ratios of 3.20 for subsequent renal pelvis cancer and 5.30 for later ureteral tumors.
The study's main strength was its large size, but limitations included the possibility of misclassifications and miscoding, an inability to account for potential confounding variables such as smoking history, family history, or treatment history, and a possibility of screening bias.
Nonetheless, Dr. Rubin and colleagues said they believe the study "reflects a true association in the population" that requires further investigation to tease out the causes.