Colorblindness May Increase The Risk Of Dying From Bladder Cancer

The team, including researchers from Stanford University, looked at the mortality rates of people with CVD in both bladder cancer and colorectal cancer. For the study, they matched cancer patients with CVD to equivalent patients with the same cancer but no CVD, and then compared the overall survival over the course of 20 years.

The researchers found no significant difference between the outcomes of patients with colorectal cancer, whether or not the patients had colorblindness. But analyzing the health records of patients with bladder cancer, the team found that patients with CVD had a 52 percent higher mortality rate (from all causes) over the course of 20 years.

So, why is that? The answer is not genetic, but about how quickly people with colorblindness are able to identify symptoms of the disease. Blood seen within urine, in the case of bladder cancer, or in your poop in the case of colorectal cancer, is one of the first signs of the disease. 

"Recognizing this sign is an essential indicator for patients to seek medical evaluation. However, patients with visual impairments that prevent them from identifying the red colour of blood in their faeces or urine may be at greater risk of delayed detection of disease," the team explains in their paper.  

"This is especially true in the case of painless haematuria, which is often the sentinel sign of bladder cancer, where blood in the urine is not accompanied by pain, which may otherwise be an alternative symptom prompting patients to seek medical attention. Without pain as an additional symptom, patients can rely solely on recognizing blood in their urine to detect the disease."

Roughly one in 12 males, or 8 percent of the total, have CVD, and 1 in 200 (0.5 percent) of females, with the majority of CVD affecting the ability to see the color red. The team was motivated by previous case studies where people with CVD misidentified blood in their stool as diarrhea, not seeking medical attention until their partners noticed the blood in the toilet and alerted them, delaying treatment by up to three months. Another study showed images of saliva, urine, and feces, and asked participants to identify which images contained blood, finding that people with CVD were significantly less successful at the task.

The team believed that there was evidence that people with CVD may miss these early symptoms, and thus may have delayed treatment, but little research had looked at whether this led to worse outcomes. Their work, which used anonymized data from around the world, found that it did for bladder cancer patients, but not for those with colorectal cancer. The team put the colorectal cancer mortality rates being roughly the same down to other symptoms being noticeable in the early stages of the disease, with nearly two-thirds of patients initially complaining about abdominal pain, and over half noticing a change in their bathroom habits.

"Blood in the stool is not the chief symptom or the most common symptom that these patients present with," senior study author Dr Ehsan Rahimy, adjunct clinical associate professor of ophthalmology at Stanford Medicine, explained in a statement.

The team hopes that the research will raise awareness in patients and doctors, with one study finding that only 10 percent of doctors had considered the possibility that patients with CVD may be less able to spot signs of blood in their urine and feces. 

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

An additional problem is that people with CVD may not know that their vision is unusual.

"Most people with color vision deficiency are typically functioning fine," Rahimy added. "They don’t have any other vision issues. Many affected individuals may not even know they have it."

While the team wants to conduct more research on the topic, they suggest that people with CVD may benefit from urine tests at annual checkups, or getting a loved one involved with looking over their bodily waste.

"If you don’t trust yourself to know that there’s a change in the color of your urine, it could be worth having a partner or somebody you live with periodically checking it for blood, just to make sure," Rahimy said.

"I’m hopeful that this study raises some awareness, not only for patients with colorblindness, but for our colleagues who see these patients," he added. "If this study raises awareness and people read this and casually pass it along, I think it’s done its job."

Other symptoms of bladder cancer include pain, burning, stinging, or itching when urinating, needing to pee more often or very suddenly, pain in the lower back and abdomen, fatigue, repeated urinary tract infections, and loss of appetite, as well as pain or tenderness in your bones.

The study is published in Nature Health.