How long can a person have cancer and not know something is wrong – Today Online with Dr Melvin Look

Cancer that has spread becomes more complicated to treat, with those in the advanced stages generally having poorer outcomes. 

People whose cancer treatment is delayed by even a month have a 6 to 13 per cent higher risk of dying — a risk that continues rising the longer treatment is put off, a study published in 2020 in peer-reviewed medical journal The BMJ suggested. 

As developed and affluent countries see higher cases of cancer among young people, it is becoming important that this group be made more aware of cancer symptoms so as not to get a delayed diagnosis.

As it is, a late diagnosis continues to be the norm in many cases despite advances in medicine. 

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For example, between 2018 and 2021, the majority of lung, stomach and pancreatic cancers were diagnosed in the later stages, based on data from the Singapore Cancer Registry Annual Report 2021.

Even for colorectal cancer, which is among the most common cancers in Singapore, more than half of the diagnoses were after the disease advanced to Stage 3 and Stage 4.  

Just how long can someone have cancer without knowing that something is seriously wrong? 

In conjunction with World Cancer Day that was on Feb 4, TODAY asked doctors why some people may not be aware that some cells in their body have gone rogue, and what are the early signs not to ignore.

Many factors can affect how early or late the cancer is detected: The type, where it is located, its speed of growth and the uptake for certain cancer screenings, the doctors said. 


Dr Melvin Look, medical director of PanAsia Surgery and specialist in gastrointestinal cancer surgery, said that it may take “months or even years” before a person experiences any symptoms. 

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He explained: “All cancers initially start at the microscopic level. Because it’s so small, it’s both asymptomatic (no symptoms) and undetectable. 

“As the tumour slowly increases in size, it may still remain asymptomatic unless a person undergoes special screening tests to look for it.” 

Eventually, the cancer grows and progresses to the “symptomatic-detectable” stage, Dr Look said.

“The symptoms are usually due to the size of the tumour itself, causing a lump that can be painful or painless. 

“The lump can also cause secondary effects like bleeding or blockage of the organ cavity where it is located.” 

For example, cancer of the upper gastrointestinal tract such as the oesophagus or stomach can cause vomiting, pain or difficulty swallowing.

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As the cancer spreads to the rest of the body, it can cause symptoms specific to the organ. For example, back pain can be a sign of secondary cancer in the bone, Dr Look added. Secondary cancer is cancer that has spread from where it first originated.


How early symptoms show up may depend on where the cancer is located and the speed of growth.


Explaining why some patients may not feel pain at first even when the cancer is growing, Dr Look said that a cancerous growth starts to cause pain or discomfort only if it invades the nearby nerves or cause a physical compression or obstruction to the organ.

“If the cancer is in an organ that has a lot of space like the stomach, the mass needs to be very large before it causes symptoms.

“On the other hand, a very early cancer can become symptomatic if it is located in an area that is visible, such as skin cancers, or they happen to produce alarming symptoms (such as bleeding from the nose in nasopharyngeal cancers),” Dr Look added. 

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Another example of a cancer that is hard to detect early due to its deep-seated location is ovarian cancer.

Dr Samuel Ow, Singapore Cancer Society’s council member and chairperson of the society’s community health committee, explained: “It’s because the ovaries are very small organs floating in the depths of the pelvis.

“On the internet, you’ll see that many people call ovarian cancer the ‘silent whisperer’, so when the patient is diagnosed with ovarian cancer by the time she has symptoms, it’s often at stage three or four.”

Dr Ow is also a senior consultant with the department of haematology-oncology at National University Cancer Institute, Singapore.


Dr Look said that some slow-growing tumours, in the thyroid or prostate for example, can remain asymptomatic for a very long time.

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Dr Ow said: “Slow-growing cancers may not just be organ-specific. Even for breast cancer, there are slower-growing types of breast cancer and faster growing types. 

“For example, triple negative breast cancers are more aggressive than mucinous breast cancer and tubular breast cancer, which are very slow-growing.”


Some people may disregard symptoms due to the mindset that “it won’t happen to me”, Dr Ow said.

“Young working individuals who are typically healthy and exercise will not be thinking that they develop cancer, but can they happen to them? Yes, of course.” 

Cancer was not on 38-year-old Nicole Tan’s mind when she started having unusual symptoms of swallowing difficulties and chest tightness late in 2020. 

“I went for medical check-ups and the doctors didn’t find anything abnormal, so I assumed that it was stress related and attributed it to anxiety. I didn’t think that it (was anything serious) at my relatively young age,” she said. 

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By April the next year, Ms Tan could no longer keep any food down, vomiting whenever she tried to eat and drink. She was rushed to the emergency department. 

It turned out to be oesophageal cancer. The oesophagus is a long muscular tube that moves food from the throat to the stomach.

“I was shocked and in disbelief for the first hour or so,” she said of what happened after she learnt of the cancer, which was at stage two or three.

Dr Look, who treated Ms Tan, said that many patients ignore symptoms because they think it is related to something commonplace such as stress or indigestion.

“Young people, tend to delay seeking medical attention because they wrongly believe that cancer only happens in older people. Unfortunately, the incidence of cancer in younger people are in fact on the rise in Singapore,” Dr Look said.

For example, the age-standardised incidence rate of cancer in the 15 to 34 age group rose by more than 40 per cent — from 27 per 100,000 population between 1993 and 1997 to 39 per 100,000 between 2013 and 2017. 

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This is based on figures from the Singapore Cancer Registry 50th Anniversary Monograph. 

Some people have “a fear of knowing” and are in denial about their health concerns, Dr Ow said. 

He once encountered a patient whose breast tumour grew so large (to about 16cm) that it broke through the skin. 


In Singapore, there are national screening guidelines for colorectal, cervical and breast cancer. These are common cancers that have proven screening strategies that affect outcomes.

“The reason for screening is because we are trying to cause what we call a stage shift,” Dr Ow explained. 

“(Cancer) screening is supposed to try to shift the needle, from a later stage to an earlier stage, with the idea that the treatment for the cancer will become less complicated, potentially cause less burden on the healthcare system and also improve overall quality of life and lifespan.”

The doctors also advised people not to ignore symptoms, especially if they have gone on for some time. 

“The key words are ‘unexplained’ or ‘persistent’,” Dr Ow said. 

“If you notice constitutional symptoms (a group of symptoms that affect many body systems) like constantly feeling tired or fatigue, unexplained weight gain or weight loss, feeling bloated, constantly feeling full or having a poor appetite, it may not be a bad idea to get a medical assessment.”