Singer Ahn Chi-hwan lost 15 kg battling stage 3 rectal cancer — here are the warning signs

Singer Ahn Chi-hwan has revealed that he lost more than 15 kilograms during treatment after being diagnosed with stage 3 rectal cancer. Rectal cancer is a malignant tumor that develops in the rectum, the final section of the large intestine, with bloody stools and changes in bowel habits among its hallmark symptoms. Because the disease often produces no clear signs in its early stages, regular screening is essential.

Ahn disclosed the experience on MBN's "Kim Ju-ha's Day and Night," which aired Saturday, saying he received the stage 3 diagnosis in 2014 and shed more than 15 kilograms during the grueling course of treatment.

He said he has since made a full recovery, describing his current physical condition as "the best of my entire life."

Rectal cancer is a form of colorectal cancer, one of the most commonly diagnosed cancers in South Korea. According to national cancer registry statistics released in 2026 by the Ministry of Health and Welfare and the Central Cancer Registry, 32,610 new colorectal cancer cases were recorded in 2023, accounting for 11.3 percent of all cancer diagnoses — the third most common cancer after thyroid and lung cancer.

Male patients outnumbered female patients by roughly 1.4 to one. By age group, people in their 60s accounted for the largest share at 26.6 percent, followed by those in their 70s at 20.0 percent and those in their 50s at 19.7 percent.

Colorectal cancer is classified as either colon cancer or rectal cancer depending on where in the large intestine it originates. Rectal cancer in particular develops close to the anus, making the preservation of bowel function and the function of surrounding organs a central challenge during treatment.

Changes in bowel habits — including bloody stools, a feeling of incomplete evacuation, and narrower stools — are the primary warning signs of rectal cancer.

The most important symptom to watch for is a change in normal bowel habits.

The rectum temporarily stores stool before expelling it through the anus. When a tumor develops there and grows, it can narrow the passage through which stool travels and disrupt normal bowel function.

The most recognizable symptom is blood in the stool, which may appear as bright red or dark red blood mixed with feces, or as blood on toilet paper after a bowel movement. Repeated bleeding can lead to iron-deficiency anemia, causing fatigue and dizziness.

A persistent feeling that the bowel has not been fully emptied — even when no stool remains — is another key symptom. A tumor irritating the inside of the rectum can create a constant urge to use the bathroom.

Stools that become noticeably thinner than before, or alternating bouts of constipation and diarrhea, are also warning signs. A sudden increase in the frequency of bowel movements or the presence of mucus in the stool may occur as well.

As the cancer advances, it can bring abdominal pain, loss of appetite, and unexplained weight loss. If the tumor severely narrows the intestine, it can cause a bowel obstruction that makes it difficult to pass stool or gas.

When such changes recur, determining the cause through a colonoscopy or other examination is important.

Bloody stools in particular are easy to confuse with hemorrhoids. People who have hemorrhoids or anal fissures also experience bleeding, and some dismiss rectal bleeding as a symptom of a pre-existing anal condition and delay getting checked.

The National Cancer Information Center advises that the color of the blood, how long the bleeding persists, and any accompanying changes in bowel habits should all be considered together.

Rectal cancer can also be detected at an early stage with no symptoms at all. A colonoscopy allows direct examination of the interior of the rectum and colon, and can identify and remove polyps that have the potential to develop into cancer.

In stage 3 rectal cancer, the disease has spread to nearby lymph nodes — and preserving the anus is a key goal of treatment.

The stage of rectal cancer is determined by how deeply the tumor has penetrated the intestinal wall, whether it has spread to nearby lymph nodes, and whether it has reached other organs.

Stage 3 generally means cancer cells have spread to the lymph nodes surrounding the rectum. The specific substage depends on the size of the tumor, the depth of invasion, and the extent of lymph node involvement.

Treatment options include surgery, chemotherapy, and radiation therapy. The sequence of treatment is decided after a comprehensive assessment of the patient's stage, tumor location, and overall condition.

In rectal cancer surgery, the goal is to remove enough cancerous tissue while preserving as much function of the anus and surrounding nerves as possible.

The rectum sits within the narrow pelvic cavity, surrounded by the bladder, reproductive organs, and nerves that govern urinary and sexual function. Depending on the extent of surgery, bowel and urinary function may be affected, making precise treatment planning essential.

When the cancer is located relatively far from the anus, surgeons can remove the tumor and reconnect the remaining sections of the intestine.

When the cancer is very close to the anus or has invaded the anal sphincter, the surgical approach must be determined with particular care.

Some patients receive chemotherapy and radiation before surgery to shrink the tumor, making it possible to preserve the anus. When the cancer has spread extensively or anal function cannot be maintained, surgery to create a colostomy — an artificial opening in the abdominal wall — may be necessary.

For advanced rectal cancer, chemotherapy and radiation are administered before surgery to reduce the tumor and lower the risk of recurrence.

Total neoadjuvant therapy — an approach that concentrates both chemotherapy and radiation in the period before surgery — has also come into use in recent years. The timing and method of surgery are determined based on how the patient responds to treatment and their overall condition.

Nutritional management is also important during cancer treatment. Chemotherapy can cause loss of appetite, nausea, diarrhea, and mouth sores, all of which reduce food intake and can lead to weight loss.

Severe weight loss depletes muscle mass and physical stamina, making it harder to tolerate treatment. That is why patients' nutritional status is monitored and they are guided to consume adequate calories and protein.

Even after surgery, patients may experience increased bowel frequency, urgency, or a feeling of incomplete evacuation. For patients who have had part of the rectum removed, dietary adjustments, medication, and bowel rehabilitation may be prescribed depending on the degree of change in bowel function.

Annual stool tests from age 50, along with healthy eating habits and regular screenings, are key to prevention.

Colorectal cancer, including rectal cancer, is influenced by lifestyle factors, genetic predisposition, and age.

Well-established risk factors include excessive consumption of red and processed meat, alcohol use, smoking, obesity, and physical inactivity. A family history of colorectal cancer or a personal history of inflammatory bowel disease also raises the risk.

The International Agency for Research on Cancer, an arm of the World Health Organization, classifies processed meats such as ham, sausage, and bacon as foods with confirmed carcinogenicity in humans.

Processed meat refers to meat that has been salted, smoked, fermented, or otherwise preserved to extend shelf life or enhance flavor. Long-term excessive consumption is associated with an increased risk of colorectal cancer.

Intake of red meats such as beef and pork should also be moderated. A balanced diet centered on vegetables, fruit, whole grains, and legumes — all rich in dietary fiber — is recommended.

Dietary fiber helps increase stool bulk and promotes regular bowel movements. Diets high in whole grains and fiber have been linked to a reduced risk of colorectal cancer.

Regular exercise and maintaining a healthy weight are equally important. Sustained aerobic activity — such as brisk walking, cycling, or swimming — and reducing prolonged sitting are advised.

Quitting smoking and avoiding alcohol are also key lifestyle measures for colorectal cancer prevention.

Regular screening plays an important role in detecting cancer before symptoms appear.

South Korea's national cancer screening program offers annual fecal occult blood tests to men and women aged 50 and older. The test checks for traces of blood in the stool that are too small to see with the naked eye.

A positive result triggers follow-up testing, such as a colonoscopy, to identify the source of the bleeding.

A colonoscopy allows direct inspection of polyps and tumors inside the colon. Detecting and removing adenomatous polyps can also help prevent some colorectal cancers from developing.

People with a close family member — such as a parent or sibling — who has had colorectal cancer, or those with inflammatory bowel disease, should discuss their individual risk with a doctor to determine when to begin screening and which tests are appropriate.

Anyone who experiences suspicious symptoms — blood in the stool, changes in bowel habits, or a persistent feeling of incomplete evacuation — should seek medical attention regardless of age or eligibility for national screening.

The scope of treatment and the prognosis for rectal cancer vary depending on when it is detected and how far it has progressed. Paying attention to changes in bowel habits and getting screened regularly can make a meaningful difference in early detection and treatment outcomes.