Color-blindness may increase bladder cancer mortality risk

Color-blind patients may be at a higher risk of bladder cancer mortality than patients who can see color, due to their inability to identify blood in their urine, which is one of the first indicators of bladder cancer, along with painless hematuria, according to the results of a study published recently in Nature Health.

A team of researchers, including corresponding author Ehsan Rahimy, Department of Ophthalmology, Stanford University School of Medicine, used the TriNetX network to gather the electronic health record data from health organizations in the United States and around the world.

Rahimy and his team identified 135 bladder cancer patients with and without colorblindness and 187 colorectal patients with and without colorblindness.

Color-blind patients with bladder cancer experienced a 52% higher 20-year mortality rate than those who could see color. However, there was no statistical significance between the rate of colorectal cancer survival and color blindness.

Color blindness is one of the most inherited visual impairment disorders, affecting approximately 1 in 12 males and 1 in 200 females in the United States. The most common type of color blindness is red-green color blindness. In these patients, red may appear dull, dark grey or black, which could hypothetically cause cancer treatment delays if patients are unable to identify blood in their waste.

The study also cites several case studies to back this hypothesis up, including one study of 10 color-blind participants and 20 age-matched controls. They were shown photographs of saliva, urine and stool and then asked to identify which photos showed blood. Only 77% of the colorblind group were able to answer correctly, compared with 99% of the control group.

Colorectal cancer and bladder cancer are two of the most common cancers in men and women in the United States. Specifically, colorectal cancer has the third-highest and fourth-highest mortality among men and women, respectively. Bladder cancer has the eighth-highest mortality among men.

The differences in risk between colorectal cancer and bladder cancer survival may be explained by symptoms and by official screening recommendations.

“A study of early-onset colorectal cancer found that 63% of patients under the age of 45 years presented with abdominal pain, 54% with a change in stool habits, 53% with rectal bleeding and 32% with weight loss and found similar findings among patients over the age of 45 years,” Rahimy and his team write. “In contrast, 80–90% of patients with bladder cancer present with painless gross hematuria, while only approximately 20% present with irritative voiding symptoms, including dysuria, urgency, frequency or urge incontinence.”

Additionally, the United States Preventive Services Task Force recommends all adults ages 45 and older be screened for colorectal cancer. However, there is no comparable recommendation for asymptomatic bladder cancer screening.

In the United States, color vision screening for school-aged children is only required in 11 states. Only Massachusetts law requires all drivers to complete a color vision test before obtaining a license, but 13 states require the test for a commercial driver’s license. This suggests that color blindness may be more prevalent than previously thought.

“Identifying the risks this may pose to survival and mortality further clarifies the importance of more attentively screening these populations for certain malignancies and may serve to increase clinicians’ suspicion of cancer among patients with CVD and signs suggesting illness,” Rahimy and his team write.