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Anal cancer risk increases due to greater exposure to virus linked to cervical cancer, multiple sex partners

SINGAPORE — When Madam Betty Ong first felt a fleshy growth around her anus in 2018, the office manager thought it might be piles. Piles or haemorrhoids are inflamed, swollen veins around the anus that can occur due to excessive straining.

Anal cancer may be overlooked because symptoms may appear similar to that of common conditions such as piles or haemorrhoids.

Anal cancer may be overlooked because symptoms may appear similar to that of common conditions such as piles or haemorrhoids.

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  • The number of anal cancer cases have increased 10 times in the last 50 years in Singapore
  • About 90 per cent of anal cancers in men and women are caused by high-risk human papillomavirus (HPV) strains.
  • Symptoms may appear similar to that of common conditions such as piles.
  • A vaccine has been approved for expanded use in middle-aged adults for the prevention of HPV-related cancers including anal cancer


SINGAPORE — When Madam Betty Ong first felt a fleshy growth around her anus in 2018, the office manager thought it might be piles. Piles or haemorrhoids are inflamed, swollen veins around the anus that can occur due to excessive straining.

Although there was slight bleeding, Mdm Ong decided to leave it alone as she did not feel unwell and was able to pass motion normally.

What she initially thought was a benign problem turned out to be a 6.4cm-large cancerous tumour.

Last year, Mdm Ong was diagnosed with Stage 3 anal cancer after she was hospitalised for an extreme bout of fever. This was around nine months after she discovered the growth.

Having completed her treatment and her cancer is now in remission, Mdm Ong told TODAY that she was shocked when she found out about her condition because she had never heard of this type of cancer.

Before her diagnosis, the grandmother-of-three, who is now in her 70s, was in good health and had never been hospitalised except for childbirth. She also does not smoke or drink.

While uncommon, anal cancer — which forms in the anal canal (at the end of the rectum) — is on the rise in Singapore.

The number of reported cases has seen a 10-fold jump in the last four to five decades, from 17 cases reported between 1968 and 1972 to 177 cases between 2013 and 2017, based on figures from the Singapore Cancer Registry.

An uptick in anal cancer cases has also been reported worldwide, including the United States and United Kingdom. And more women than men have it.


The American Cancer Society said that women who have had cancer of the cervix, vagina, or vulva are at increased risk of anal cancer. This is probably because these cancers are also caused by infection with the human papillomavirus (HPV).

Like cervical cancer, the majority of which is caused by high-risk HPV strains, anal cancer is preventable.

Dr Julian Ng, resident doctor at DTAP Clinic, said that the virus causes around 90 per cent of anal cancers. Certain groups of HPV viruses can also cause genital warts.

Dr David Tan, consultant radiation oncologist at Asian American Radiation and Oncology and Concord International Hospital, said that one of the reasons for the jump in cases is due to an increase in HPV exposure, which could be related to evolving sexual practices.

For example, an increase in the number of sexual partners and practice of receptive anal intercourse, he said.

“Having more sexual partners mean a higher risk of exposure to the high-risk strains of HPV, which can cause anal cancer. HPV is spread via skin-to-skin contact; the chance of being infected occurs when the virus enters through a cut, abrasion or small tear in the skin,” Dr Tan said.

Dr Ng said that men who have sex with men, or women who have male partners who engage in anal sex without a condom, are more likely to be infected at the anus and thus at a higher risk of developing anal cancer. 

Dr Tan said that another factor for the rise in anal cancer numbers is immunosuppression (suppression of the immune system), which results in an impaired ability to eradicate the virus before it causes cancer.

A human immunodeficiency virus (HIV) infection, taking immunosuppressive drugs for chronic medical conditions and age are some factors that can impair the body’s immune function. Anal cancer is more common in the older age group above 50.

Smoking as well as those who have had cervical, vulvar or vaginal cancer also have an increased risk of developing anal cancer.


As symptoms may appear similar to that of common conditions such as piles, anal cancer may be overlooked.

For example, both piles and anal cancer can cause bleeding or pain in the anus, sometimes accompanied by a mass.

Patients may also get constipation if the mass obstructs the anal canal, Dr Tan said. There may also be itching in the anal area.

“What is most important is for people to see a doctor, anytime they notice these symptoms, for a clinical examination. Tumour masses tend to grow with time, become harder and irregular in shape and bleed more easily than pus. Such assessments are, however, best made by a medical professional,” Dr Tan said.

Similar to other cancers, the earlier anal cancer is detected, the higher the survival rate.

The five-year survival rate for early-stage anal cancer is 85 per cent but this drops to 15 per cent for Stage 4 patients whose cancer has spread to distant organs, such as the liver and lungs, Dr Tan said.

About two in five patients are diagnosed in the late stages.

Dr Tan also said that early-stage anal cancer can be treated with surgery to excise the mass while the later stages are generally treatment with radiotherapy combined with chemotherapy.


While there is no sure way to prevent anal cancer, certain measures can reduce the risk of HPV transmission. Dr Ng from DTAP Clinic said that these include safe sex practices such as wearing of condoms and being in a monogamous relationship. However, he pointed out that condoms only cover the penis.

“For HPV that is located in other surrounding areas, such as the scrotum area or in females, the labia or pubic area, the transmission can still occur. That is how, in many cases, genital warts can be transmitted despite condom use,” Dr Ng said.

Vaccines to protect against HPV infections are available.

In September this year, the Health Sciences Authority approved the HPV vaccination Gardasil 9 for use by males and females aged nine to 45 —for the prevention of HPV-related cancers and diseases including anal cancer caused by certain high-risk strains.

It can also protect against genital warts in both men and women. Previously in Singapore, it was indicated for individuals aged nine to 26 years.

Dr Tan from Concord International Hospital said that the vaccine can reduce the risk of anal pre-cancer lesions caused by HPV by around 80 per cent.

While the vaccine works best when individuals are vaccinated before they become sexually active, the doctors said that adults who already had prior sexual exposure can still get some protection against other HPV strains to which they may not have been exposed.

“The 80 per cent risk reduction will vary according to the extent that the individual has been exposed to the high-risk strains.

“In adults who have already had sexual intercourse and exposure to certain high-risk HPV strains, the vaccine will not be protective against those strains,” Dr Tan said.

“However, it is unlikely that they would have been exposed to all types of HPV contained in the vaccine so it will still benefit them.”

Dr Ng’s advice to adults is to “strongly consider” getting the vaccine to not only protect themselves but also reduce the risk of their loved ones getting infected through sexual contact with them, since the vaccine can protect a person from cervical cancer, anal cancer and genital warts.

He added that the group of HPV viruses that causes genital warts is different from those that cause cervical or anal cancer, and vice versa.

Dr Ng also said that there are other HPV vaccines available, such as Cervarix or Gardasil (4-valent HPV vaccine), but they do not offer protection against the same number of strains of HPV as Gardasil 9.

Three doses are required over the course of six months and each dose may cost around S$200 and above, depending on the clinic.

The cost of the Gardasil 9 vaccine cannot be claimed through MediSave, the national savings account for medical expenses under the Central Provident Fund.

However, Cervarix or Gardasil (4-valent HPV vaccine) can be paid through MediSave for females aged nine to 26.

Havig learnt that the majority of anal cancers can be prevented, Mdm Ong encouraged adults to get vaccinated to protect themselves.

For her treatment, she underwent intensive chemotherapy and radiation for five to six weeks, during which she kept her condition a secret from her social circle.

She experienced side effects of treatment such as swelling in her wrists due to multiple injections and the inability to sit properly due to pain in the anal area, but she tried her best to continue with her daily life.

She worked from home and continued to attend church meetings.

“My friends thought I had piles. I kept my condition a secret for as long as I could because I did not like people to feel sorry for me or ask me many questions,” she said.

“When I finally made an announcement (about the cancer), everyone was shocked.”

Life has returned to normal for Mdm Ong, whose cancer is now in remission and she credits her recovery to the medical team caring for her, as well as support from her loved ones.

She said that her faith and accepting that there are “sunshine and stormy days” in life have kept her going during her cancer journey.

“I am thankful that I am leading an abundant life and my cancer is not that bad after all. I count my blessings daily.” 

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