It's been dubbed the 'silent killer' and will strike one in eight men in their lifetimes.

For men over 70, the risk is one in two. 

Yet prostate cancer is one of the most curable forms of the disease when caught early, with nearly a 100 percent survival rate if detected while localized in the prostate.

Dr. William Dahut, the chief scientific officer at the American Cancer Society who has spent 20 years researching prostate cancer, warned most people diagnosed have no idea they have the cancer until it's too late.

Its mild symptoms - fatigue and waking up often to urinate - are often dismissed and it's not until the cancer spreads that more serious side effects occur.

Most patients have no symptoms, he told the Daily Mail. 'If they do have symptoms, like increased urination or getting up in the night to urinate, they think these are due to something else.'

In former President Joe Biden's case, his late-stage cancer wasn't detected until he developed urinary symptoms. 

Cases of the cancer are rising among all ages, up by 3 percent year on year, including young adults. There's been a worrying rise in the under-40 age group of about 2 percent every year globally since the 1990s.

And more men are getting diagnosed later, when the disease is harder to treat, with late stage diagnoses rising 5 percent per year since 2011.

Former president Joe Biden, 82, revealed on Sunday that he had been diagnosed with aggressive prostate cancer. He is pictured above yesterday

Doctors have blamed confusion over screening guidelines for this shift, saying it led many to miss potentially life-saving appointments. 

Biden revealed his diagnosis in a message on Sunday, saying there was a 'lump' on his prostate and that the cancer was 'aggressive' and spread to his bones.

His family say they are now reviewing treatment options for the 82-year-old. 

What is prostate cancer?

Prostate cancer is when cells start to divide uncontrollably in the prostate, a walnut-sized gland.

The prostate is located just below the bladder and in front of the rectum and produces fluid used in semen.

It gradually increases in size as someone ages, and by the time they're 60, it is often the size of a lemon - leading to a variety of complications.

The cancer only affects people with a prostate. 

For about one in eight men, it can also develop cancer, according to the American Cancer Society (ACS).

This is often slow-growing and easy to treat, with a good prognosis of more than 99 percent of patients surviving five years.

But if it spreads, it becomes much harder to treat. Then, only 37 percent of patients survive for five years after diagnosis.

Biden has been diagnosed with an 'aggressive' cancer, that has a Gleason score of nine (out of 10).

'While many cases are slow-growing and caught early, aggressive subtypes, like Gleason eight to 10, can progress rapidly and require fast treatment,' Dr. Tiffany Troso-Sandoval, a medical oncologist in New York City, told the Daily Mail.

'As oncologists, we often quote that men more frequently die with prostate cancer rather than from it. Yet age alone doesn't determine aggressiveness of outcome.'

Is prostate cancer becoming more common?

Cases of prostate cancer are rising.

From 2014 to 2019, studies found that cases across all age groups rose by about 3 percent annually. They are now expected to double between 2020 and 2040.

Data shows that the rate of prostate cancer diagnoses by stage at diagnosis. It shows a slight uptick in diagnoses at a later stage (purple line)

The above shows age at diagnosis with prostate cancer. There has been a very slight uptick among younger groups

About 313,780 people are diagnosed with prostate cancer in the US every year, while about 35,770 die from the disease.

This is lower than in the 1990s, when there were about 500,000 cases per year, but higher than in 2014, when the figure was 233,000.

The cancer commonly affects men older than 65, who make up about six in 10 cases.

According to a 2019 study, global cases of prostate cancer among people 15 to 40 years old have risen by 2 percent since 1990.

Dr. Dahut said prostate cancer is rare among young adults, but not as rare as someone might think. 

In 2001, 7 percent of cases were among young adults, according to the CDC - now, it's 9 percent. Men in their 30s, for example, are being increasingly diagnosed.

But this trend isn't just limited to prostate cancer, Dr. Dahut tells the Daily Mail.

It's not clear why cases are rising in younger age groups, but doctors have named rising obesity rates and sedentary lifestyles as potential factors.

There is also a worrying uptick in the number of advanced diagnosis. 

Biden is pictured above with President Donald Trump amid the handover of power in the Oval Office

A study from California showed advanced cases in the state rose 6.7 percent on average from 2004 to 2021. 

Initially, men were screened for the cancer using a prostate-specific antigen, or PSA, test which caught numerous cancers in the earliest stages.

But in 2012, the US Preventative Services Task Force recommended against using the test over fears of false positives and unnecessary procedures.

It U-turned again in 2017, saying people aged 55 to 69 should ask their doctors about getting the test.

The American Urological Association does not recommend screening for the cancer to over-70s because the cancer grows so slowly and doctors say other illnesses are likely to prove lethal first.

But that recommendation has raised concerns that emerging and aggressive tumors could be missed.

Doctors have suggested Biden may have been too old or frail to be tested for prostate cancer in recent years, which is how the disease went undetected. 

How likely is survival?

If prostate cancer is caught in the earliest stages, patients generally have a good chance of survival.

According to the CDC, about 69 percent of cases are diagnosed at the local stages, or stage one to three (before the cancer has spread beyond the prostate).

For comparison, 9 percent of patients are diagnosed at the distant stage (when the cancer has spread to other areas of the body).

The ACS says nearly all patients survive when the cancer is diagnosed between stages one and three, but that chance drops to 37 percent in later stages.

The above shows the survival rate for prostate cancer. It drops when it is diagnosed at a later stage

Survival rates for prostate cancer appear to have dipped slightly over recent years, amid a rise in the number of people being diagnosed with an advanced form of the disease

Dr. Dahut said it can be a 'little frightening' for men to be diagnosed with the cancer, but calls survival rates encouraging.

Biden's cancer is distant, having already spread to his bones, and has been described as 'aggressive'.

It is understood that his family is reviewing treatment options.

Dr. Dahut said later stages are difficult as disease has already spread to organs - like heart and lungs. Some doctors say once it reaches those organs, it is 'incurable'.

Treatments rely mainly on a drug that blocks testosterone production, but over time cells develop resistance to it. 

The risk of developing prostate cancer rises as you age. Those over 70 have a 50 percent chance of developing it.

What are the warning signs of prostate cancer?

Prostate cancer is often called a 'silent cancer', as it rarely cause symptoms - when it does, they're nonspecific or pass for another condition.

The Mayo Clinic says there are potential warning signs in the early stages: blood in urine (may look pink, red or colada-colored), blood in the semen, needing to urinate more often, trouble getting started while urinating and waking up to urinate more often at night.

In the later stages, when it has spread to other areas of the body, it may trigger other symptoms: accidental leaking of urine, back pain, bone pain, difficulty getting an erection, feeling very tired, losing weight without trying and weakness in the arms and legs.

Is there anything I can do to monitor for prostate cancer?

Doctors already have screening guidelines in place to help detect prostate cancer before it becomes advanced.

All men are recommended to get screened for the cancer by at least age 50, and at 45 if they have a family history.

They may then be asked to return for screening every one to two years for checkups.

Guidelines vary for when people should stop getting screened.

Dr. Dahut said despite the confusion over when to stop screening, doctors and patients are asked to use their 'clinical judgement' to decide.

He said in cases where someone has multiple underlying conditions or there is concern about their overall health, doctors may stop monitoring for prostate cancer. 

In addition to PSA, doctors may also carry out the digital rectal exam, where a lubricated, gloved finer is placed into the rectum to reach the prostate - enabling someone to judge if it has abnormal lumps or hard areas.

What are the treatment options?

In the early stages, patients tend to be offered active surveillance or regular monitoring of their cancer.

Patients may also be offered radiation therapy or surgery to remove the cancer, but this can lead to life-long complications such as trouble urinating. 

If the cancer shows signs of spreading, patients may be offered surgery or radiation therapy.

In cases where the cancer has spread to other areas of the body, patients may be offered a variety of treatments including external beam radiation treatment, where external beams of radiation are fired on the prostate to kill the cancer cells.

A radical prostatectomy, surgery to remove the entire prostate glad and surrounding tissue and lymph nodes, is also an option.

Patients can also select hormone therapy with drugs like abiraterone, working by reducing testosterone levels that slow the growth of the cancer.