Serious delays have been seen in breast cancer diagnosis among women living in the northern coastal area of Fukushima devastated by the March 2011 earthquake-triggered tsunami and ensuing nuclear disaster, according to a study by a local doctor.

After the crisis, the proportion of women who consulted with doctors more than three months after noticing breast cancer symptoms rose to 29.9 percent of those who consulted with them about symptoms, compared with 18.0 percent before the disaster, the study found.

Many women who saw a doctor about their symptoms only did so after being encouraged by family members, according to the study. A rise in the number of single-person households and that of those composed only of elderly couples due to protracted evacuation is believed to be behind the trend.

The study was conducted by Akihiko Ozaki, a doctor at Minamisoma Municipal General Hospital in Minamisoma, Fukushima Prefecture, after he noticed that many women began visiting him after their symptoms had progressed.

Early diagnosis is the key to breast cancer treatment. If it takes a woman three months or longer to see a doctor after first noticing symptoms, she is said to face a poor prognosis.

A doctor with knowledge of medical conditions in disaster-affected areas says similar problems could occur in other areas hit by disasters or the Tokyo metropolitan area, where the population is graying just as the rest of the country.

In Japan, breast cancer is the most common cancer for women. Around 13,000 people die of it every year. The number of breast cancer patients including young women has been rising, and the issue has attracted renewed attention after popular TV personality Mao Kobayashi recently died of the disease at age 34.

Ozaki's research, published in a British journal on cancer, covered a total of 219 breast cancer patients who, after noticing such symptoms as a lump, visited either of two hospitals in the city of Minamisoma between 2005 and 2015. Of those, 122 visited the hospitals before the disaster, while 97 did so after that.

The figures exclude patients who were diagnosed with cancer in health examinations. The average age of the patients before the disaster was 62 compared with 63 after the calamity.

Of the patients who did not see doctors until at least three months after first noticing symptoms, 37.9 percent were living in the households of their son or daughter. Of the patients who saw doctors less than three months after first noticing symptoms, 51.5 percent were living in similar households.