What Is Cancer? Types, Stages, Risk Factors and Cancer Statistics in Japan & New Zealand

When people hear the word “cancer”, they may immediately think of a frightening disease or the often-quoted statistic that around one in two people in Japan will develop cancer during their lifetime.

Cancer is, in fact, a very common health issue in Japan.

According to the National Cancer Center Japan’s latest cancer statistics, the lifetime risk of being diagnosed with cancer is 61.1% for men and 50.1% for women. In other words, for both men and women, the lifetime risk is approximately one in two.

However, “cancer” is not a single disease. There are many different types, including lung cancer, stomach cancer, colorectal cancer, breast cancer, prostate cancer and leukaemia. Their characteristics vary depending on where they develop and the type of cells involved.

You may also have heard terms such as “Stage I”, “Stage IV”, “metastasis” and “five-year survival rate” without being entirely sure what they mean.

This article explains the basics in an easy-to-follow way, including what cancer is, the different types of cancer, and what cancer stages mean.

We will also look at the latest statistics on the most commonly diagnosed cancers in Japan and then compare them with the cancer patterns seen in New Zealand.

There are some interesting differences between the two countries. In particular, melanoma, which does not rank among the most commonly diagnosed cancers in Japan, is one of the major cancers diagnosed in New Zealand.

If you are beginning to research cancer and are unsure where to start, this article is designed to provide a useful overview of the key concepts and terminology.

What Is Cancer? The Basics to Know First

The human body is made up of a vast number of cells.

Normal cells have mechanisms that regulate when they grow, divide and stop dividing. Genes inside our cells play an important role in controlling these processes.

Changes in genes can sometimes occur by chance when cells divide. Genetic changes can also result from external influences such as tobacco smoke, certain viral or bacterial infections, some chemicals and radiation.

When these genetic changes accumulate, cells may lose the normal controls that regulate their growth and begin to multiply in an uncontrolled way.

A mass of cells formed in this way is called a tumour.

However, not every tumour is cancer.

What Is the Difference Between a Benign and Malignant Tumour?

Tumours are broadly classified as benign or malignant, depending on characteristics such as how they grow and whether they spread into surrounding tissues.

Benign tumours generally do not invade surrounding tissue or spread to distant parts of the body.

Malignant tumours, on the other hand, may grow into surrounding tissue, known as invasion, and cancer cells may also spread through the blood or lymphatic system to other parts of the body, known as metastasis.

In a broad sense, malignant tumours are what we refer to as cancer.

An important point is that a single genetic change does not mean that a cell will immediately become cancerous.

For many cancers, several genetic changes are thought to accumulate over a long period before a normal cell becomes a cancer cell. This is sometimes described as multistep carcinogenesis.

This gradual accumulation of genetic changes is also one of the reasons why many types of cancer become more common with increasing age.

Cancer Itself Is Not Contagious

Certain viral and bacterial infections are associated with an increased risk of particular cancers.

Examples include human papillomavirus (HPV) and cervical cancer, Helicobacter pylori and stomach cancer, and hepatitis B and C viruses and liver cancer.

However, cancer itself does not spread from person to person through coughing, sneezing or ordinary physical contact.

It is important to distinguish between “an infection that can increase the risk of certain cancers” and “cancer itself being infectious”.

What Types of Cancer Are There?

Many cancers are commonly named according to the organ in which they first develop, such as stomach cancer, lung cancer and colorectal cancer.

Medically, however, cancers can also be classified according to the type of cell from which they arise, not only the organ in which they are found.

In Japanese, “がん” and “癌” Do Not Have Exactly the Same Meaning

In everyday Japanese, the hiragana word “がん” and the kanji “癌” are often used almost interchangeably, but medically there is a subtle distinction.

The National Cancer Center Japan explains that “がん” is a broad term covering malignant tumours generally, while “癌” refers mainly to malignant tumours arising from epithelial cells.

For example, leukaemia and sarcomas are included within the broader concept of “がん”, but in Japanese they would not normally be described using “癌” in the same way as stomach or colorectal carcinoma.

Broad Categories Include Carcinomas, Sarcomas and Blood Cancers

Many cancers, such as stomach and lung cancers, form solid tumours.

Other cancers, such as leukaemia, generally do not form a solid lump in the same way. Instead, abnormal cells develop within the blood or bone marrow.

Therefore, cancer does not always mean that a physical lump or solid tumour will be present somewhere in the body.

What Happens to the Cancer’s Name When It Spreads?

Two terms that can be confusing when first learning about cancer are primary cancer and metastasis.

For example, if cancer begins in the stomach and later spreads to the lungs, it does not become a newly developed lung cancer.

Instead, it is considered stomach cancer that has metastasised to the lungs.

Cancers are generally classified according to the primary site where they first developed.

This distinction is important when treatment is being considered because the characteristics of the cancer cells and the available treatment options depend on the original cancer, not simply on the organ to which it has spread.

What Do Stages 0, I, II, III and IV Mean? Understanding TNM Staging

When reading about cancer, terms such as “Stage I”, “Stage III” and “Stage IV” appear frequently.

Cancer stage describes how far the cancer has spread within the body.

Staging generally considers factors such as the size and extent of the primary tumour, whether nearby lymph nodes are involved, and whether cancer has spread to distant organs.

What Is the TNM Classification?

One widely used staging system for many solid cancers is the TNM classification.

The combination of T, N and M findings helps determine the stage.

However, the same staging criteria are not used for every type of cancer.

For example, the exact meaning of “Stage II” differs between stomach, breast and lung cancers. Leukaemias and some brain and spinal tumours may use other classification systems rather than the conventional TNM system.

What Do Stages 0 to IV Generally Mean?

Many solid cancers are grouped into stages from Stage 0 to Stage IV.

This table is only a broad guide to understanding staging.

In practice, each cancer type has its own detailed criteria. Stages may also be subdivided, for example into IA and IB, or IIIA, IIIB and IIIC.

For this reason, it is not accurate to assume that every Stage II cancer has the same outlook, or that every Stage IV cancer represents exactly the same clinical situation.

The type and location of the cancer, molecular and genetic characteristics, age, general health and response to treatment can all influence an individual situation.

Stage and Grade Are Different

Another pair of terms that are easily confused are stage and grade.

Stage mainly describes how far the cancer has spread in the body.

Grade, on the other hand, describes features of the cancer cells and tissue seen under a microscope, including how different they appear from normal cells.

Depending on the cancer type, grade and molecular or genetic features may also be important when treatment options are considered.

Which Cancers Are Most Common in Japan? A Look at the Latest Statistics

So which types of cancer are most commonly diagnosed in Japan?

The following figures are based on the latest published data from the National Cancer Center Japan.

Around 993,000 New Cancer Diagnoses Were Recorded in Japan in 2023

According to Japan’s National Cancer Registry, 993,469 cancer cases were newly diagnosed in 2023.

This included 556,059 cases among men and 437,406 among women.

Meanwhile, vital statistics show that 384,111 people died from cancer in 2024, including 221,786 men and 162,325 women.

It is important to recognise that the number of newly diagnosed cases and the number of cancer deaths are different statistical measures.

Cancers differ in how common they are, how they progress and how they are treated, so the most commonly diagnosed cancer is not necessarily the cancer responsible for the most deaths.

“Around One in Two People in Japan Will Develop Cancer” Is Still Broadly Accurate

Using 2023 data, the National Cancer Center Japan estimates the lifetime risk of being diagnosed with cancer as:

• Men: 61.1% — approximately 1 in 2
• Women: 50.1% — approximately 1 in 2

So the widely used statement that “around one in two people in Japan will be diagnosed with cancer during their lifetime” remains broadly consistent with the latest statistics.

However, another older phrase — that “one in three people in Japan will die from cancer” — is no longer consistent with the latest lifetime-risk statistics.

Based on 2024 data, the estimated lifetime risk of dying from cancer is:

• Men: 24.4% — approximately 1 in 4
• Women: 17.2% — approximately 1 in 6

Cancer statistics change over time as population structure, cancer incidence, diagnosis and treatment evolve. When you see a statistic expressed as “one in X people”, it is therefore important to check which year’s data it is based on.

Most Commonly Diagnosed Cancers Among Japanese Men in 2023

By number of diagnoses, the top five cancers among men in Japan in 2023 were:

Stomach cancer was historically very common in Japan, so some people may still associate it with being the most common cancer among Japanese men.

However, based on 2023 incidence figures, prostate cancer now ranks first among men.

Most Commonly Diagnosed Cancers Among Japanese Women in 2023

The ranking among women looks different.

Breast cancer is the most commonly diagnosed cancer among women, followed by colorectal, lung, stomach and uterine cancers.

When men and women are combined, colorectal cancer ranks first in Japan in 2023, followed by lung cancer and stomach cancer.

Mortality Rankings Are Not the Same as Incidence Rankings

Now let us look at cancer deaths in 2024.

Among men, prostate cancer ranks first for incidence but does not appear in the top five causes of cancer death. Lung cancer, meanwhile, ranks third in incidence but first in mortality.

Among women, breast cancer ranks first in incidence but fourth in cancer deaths, behind colorectal, lung and pancreatic cancers.

This illustrates that “how often a cancer is diagnosed” and “how many people die from that cancer” are different measures.

Different cancers vary in when they are usually detected, how they progress and what treatment options are available.

But are the same types of cancer common in other countries?

In the next section, we compare Japan with New Zealand using the latest available 2023 New Zealand Cancer Registry data.

Looking at the two countries using data from the same year reveals both similarities and some interesting differences.

One of the most striking differences is melanoma.

Melanoma does not rank among the leading cancers in Japan, but it is one of the major cancers diagnosed in both men and women in New Zealand.

How Do Common Cancers Differ Between Japan and New Zealand?

As we have seen, colorectal, lung, stomach, breast and prostate cancers are among the cancers commonly diagnosed in Japan.

So what does the picture look like in New Zealand when we use statistics from the same year, 2023?

According to the latest New Zealand Cancer Registry data published by Health New Zealand | Te Whatu Ora, 29,719 new cancer registrations were recorded in New Zealand in 2023.

The three most commonly registered cancers among men were:

• Prostate cancer: 4,782 cases
• Melanoma: 1,881 cases
• Colorectal cancer: 1,785 cases

Among women, the top three were:

• Breast cancer: 3,878 cases
• Colorectal cancer: 1,653 cases
• Melanoma: 1,520 cases

For a reader familiar with Japanese cancer statistics, the most noticeable feature is again melanoma.

In Japan’s 2023 statistics, the top three cancers among men were prostate, colorectal and lung cancer, while among women they were breast, colorectal and lung cancer.

In New Zealand, however, melanoma ranked second among men and third among women.

Comparing Japan and New Zealand in 2023

Putting the top three cancers for men and women side by side makes the differences easier to see.

Both countries have high numbers of prostate, breast and colorectal cancers, but melanoma is far more prominent in New Zealand’s cancer profile.

Stomach cancer also ranks highly among both men and women in Japan, but it does not appear among New Zealand’s top three cancers.

These patterns show that the types of cancer commonly diagnosed can differ between countries.

However, this comparison should not be interpreted to mean that an individual person is automatically “more likely” to develop a particular cancer simply because they live in Japan or New Zealand.

Countries differ in population age structure, ethnicity, genetic background, lifestyle, patterns of infection, environmental exposure, screening and diagnostic practices.

Although both countries are compared here using 2023 registry data, their population structures and cancer-registration methods are not identical. The purpose of this comparison is therefore not to rank which country has a “higher” cancer burden, but to look at which types of cancer are commonly diagnosed in each country.

Melanoma Accounts for Around 10% of Registered Cancers in New Zealand

The New Zealand cancer control agency, Te Aho o Te Kahu | Cancer Control Agency, published “The State of Cancer in New Zealand 2025” on 11 December 2025. The report summarises the distribution of cancers diagnosed between 2018 and 2022.

According to the report, prostate cancer accounted for 16% of registrations, breast cancer 13%, colorectal cancer 12%, followed by melanoma at 10%.

This means that melanoma remains one of New Zealand’s major cancers not only in the single-year 2023 figures, but also when several years of data are considered together.

What Is Melanoma, a Cancer That Stands Out in New Zealand?

So what exactly is melanoma, which appears so prominently in New Zealand cancer statistics?

Melanoma is a cancer that develops from cells called melanocytes.

Melanocytes produce the pigment melanin and are found in the skin and some other tissues.

Most melanomas develop in the skin, but “skin cancer” does not mean the same thing as “melanoma”.

Other types of skin cancer include basal cell carcinoma and squamous cell carcinoma.

A Mole and Melanoma Are Not the Same Thing

When researching melanoma, you will often see information about moles.

Having an ordinary mole does not mean that it is melanoma.

However, changes in an existing mole or patch of skin that may warrant medical assessment include:

• becoming asymmetrical
• developing an irregular border
• developing uneven or changing colour
• changes in shape, colour, size or texture
• bleeding, itching or pain
• a new or unusual spot appearing on the skin

These changes do not necessarily mean melanoma is present, but it is important not to rely on self-diagnosis if you notice a new or concerning skin change.

Te Aho o Te Kahu also advises people to speak with a doctor if they notice a new or changing skin lesion that concerns them.

New Zealand Has One of the World’s Highest Melanoma Rates

“The State of Cancer in New Zealand 2025” describes New Zealand, together with Australia, as having one of the highest melanoma incidence rates in the world.

The report states that more than 95% of melanoma cases in New Zealand are associated with exposure to ultraviolet (UV) radiation from the sun.

Melanoma rates also differ considerably between population groups within New Zealand. Rates are particularly high among people classified as European/other, and melanoma is also more common among men and older adults.

This does not mean that everyone living in New Zealand faces the same level of melanoma risk. UV exposure, skin type, age, previous sunburn, genetic background and other factors all need to be considered.

Why Is UV Radiation So Strong in New Zealand?

If you have lived in New Zealand, you may have felt that the sunlight seems stronger than in Japan.

New Zealand’s Ministry for the Environment states that peak summer UV levels in New Zealand are roughly 40% higher than at comparable latitudes in the Northern Hemisphere.

Expressed as a ratio, this is approximately 1.4 times as high.

Factors contributing to this include:

• the Earth being relatively closer to the Sun during the Southern Hemisphere summer
• the ozone layer above New Zealand being thinner in summer than over comparable Northern Hemisphere latitudes
• relatively clean air, with fewer atmospheric particles to absorb or scatter UV radiation

When we compare cancer patterns in Japan and New Zealand, it becomes clear that the UV environment is one important factor to consider when looking at why melanoma is such a prominent cancer in New Zealand.

However, differences in melanoma incidence between countries cannot be explained by UV radiation alone.

Skin type, genetic background, age, history of sunburn, time spent outdoors, sun-protection behaviours and population structure can all play a role.

What Are the Main Risk Factors for Cancer?

When asking “Why does cancer develop?”, there is not always a single clear answer.

For many cancers, several factors may be involved, including ageing, lifestyle, environmental exposures, infections and genetic factors.

For this reason, cancer information often uses the term “risk factor” rather than simply “cause”.

Having a risk factor does not mean that a person will definitely develop cancer. Conversely, cancer can occur even when no obvious known risk factor is present.

Age

Age is an important risk factor for cancer overall.

As we get older, cells have had more opportunities to accumulate genetic changes, and the incidence of many cancers rises with age.

This does not mean that younger people cannot develop cancer. The age groups most commonly affected vary between cancer types.

Smoking

Smoking is one of the best-established risk factors for cancer.

It is associated not only with lung cancer but also with cancers of the mouth and throat, larynx, oesophagus, stomach, pancreas, bladder and several other sites.

Second-hand smoke can also affect health. The National Cancer Center Japan’s cancer-prevention guidance therefore includes not smoking and avoiding exposure to other people’s tobacco smoke.

Alcohol

Many studies have examined the relationship between alcohol consumption and the risk of certain cancers.

Alcohol is associated with cancers including those of the mouth and throat, oesophagus, liver, colorectum and breast. From the perspective of cancer risk, keeping alcohol consumption low is recommended.

Diet, Physical Activity and Body Weight

Diet, physical activity and body weight have also been studied in relation to the risk of certain cancers.

However, it is not appropriate to assume that “eating one particular food will prevent cancer” or that “one particular food caused a cancer”.

The National Cancer Center Japan groups lifestyle and infection-related measures into its “5+1 Recommendations for Cancer Prevention for Japanese People”, which we explain in more detail in the next section.

Viral and Bacterial Infections

Certain infections are important risk factors for some cancers.

Examples include:

• human papillomavirus (HPV) and cervical cancer, among others
• Helicobacter pylori and stomach cancer
• hepatitis B and C viruses and liver cancer

Not everyone with one of these infections will develop cancer. However, infection prevention, vaccination, appropriate testing and medical care can reduce the risk of some infection-related cancers.

Ultraviolet Radiation

UV radiation is an important risk factor for skin cancer, particularly melanoma.

In New Zealand, sun-safety recommendations include avoiding severe sunburn, using clothing, hats and shade, applying sunscreen appropriately and avoiding sunbeds.

Inherited Genetic Factors

Some people inherit genetic changes that increase their susceptibility to certain cancers.

However, having a family member who has had cancer does not mean that you will inevitably develop cancer yourself.

Most cancers cannot be explained by inherited factors alone. Genetic changes acquired with age and lifestyle or environmental influences also contribute.

Stress Should Not Be Treated as a Single Direct Cause of Cancer

There is ongoing research into stress and health, but it is not appropriate to conclude that “a person developed cancer directly because they experienced stress”.

It is also inappropriate to suggest to someone with cancer that their illness occurred because they “were too stressed” or because of their personality.

Cancer is influenced by many factors, and an individual case cannot usually be reduced to one lifestyle habit or psychological state.

Can Cancer Be Prevented? Screening and Early Detection

Many people understandably want to know what they can do to avoid developing cancer.

The first point to understand is that there is currently no way to prevent every cancer completely.

The National Cancer Center Japan explains cancer prevention not as reducing cancer risk to zero, but as reducing the likelihood of developing cancer.

Japan’s “5+1” Cancer-Prevention Recommendations

Based on research involving Japanese populations, the National Cancer Center Japan summarises evidence-based lifestyle and infection-related measures as the “5+1 Recommendations for Cancer Prevention for Japanese People”.

The important point is not to assume that following these recommendations means you will “definitely never get cancer”.

Rather, they provide a way to understand modifiable risk factors and reduce risk where possible.

Prevention and Early Detection Are Not the Same Thing

Cancer prevention and early detection are often discussed together, but they refer to different concepts.

Prevention aims to reduce the risk of developing cancer in the first place.

Cancer screening, on the other hand, is generally offered to people without symptoms in order to detect certain cancers earlier and reduce cancer-related mortality.

If a screening test results in a recommendation for further investigation, this does not mean that cancer has already been diagnosed.

Additional examinations are required to determine whether cancer is present.

Main Cancer Screening Programmes Recommended in Japan

According to National Cancer Center Japan information updated on 1 April 2026, population-based cancer screening in Japan primarily focuses on the following five cancers:

• Stomach cancer screening
• Colorectal cancer screening
• Lung cancer screening
• Breast cancer screening
• Cervical cancer screening

The recommended age, test method and screening interval differ depending on the cancer. Implementation may also vary between local authorities.

For that reason, screening is not simply a matter of “having every available test every year”. It is important to check the recommended age range, method and interval for each screening programme.

If You Have Symptoms, Seek Medical Advice Rather Than Waiting for Screening

Another important point is that routine cancer screening is generally intended for people who do not have symptoms.

If you already have a physical symptom or change that concerns you, it is important not to simply wait until your next scheduled screening appointment.

For example, persistent changes such as blood in the stool, coughing up blood, a lump, unusual bleeding, a persistent cough or unintentional weight loss should be discussed with an appropriate healthcare professional.

Key Cancer Terms Worth Knowing

Finally, here are several terms that can make cancer statistics and medical information easier to understand.

Incidence, Number of Cases and Incidence Rate

Incidence refers to newly diagnosed cases of a disease. The number of cases is the number of new diagnoses, while the incidence rate describes how often new cancers occur within a defined population.

When countries or regions are compared, simple case numbers can be misleading because populations differ in size and age structure. Measures such as incidence per 100,000 people and age-standardised incidence rates are therefore often used.

Number of Deaths and Mortality Rate

The number of deaths refers to how many people died from a particular cancer, while the mortality rate describes the number of deaths relative to a defined population.

Primary Cancer, Metastasis and Recurrence

The primary cancer is where the cancer first developed. Metastasis means the cancer has spread from that original site to another part of the body. Recurrence means cancer is detected again after treatment.

Stage

Stage describes how far a cancer has spread. The specific staging system and criteria vary according to cancer type.

Five-Year Survival Rate

The term “five-year survival rate” can sometimes sound as though it means “the probability that someone will live for only five years”, but that is not what the statistic means.

A five-year survival rate is a statistical measure describing survival among a group of people for a defined period following diagnosis.

According to the National Cancer Center Japan’s latest cancer statistics, the five-year relative survival rate for all cancers combined among people diagnosed in 2018 was 64.8%.

However, this combines all cancer types. Survival rates vary considerably according to cancer type, age, stage and other factors.

Survival statistics are also based on groups of people diagnosed in the past and do not predict an individual person’s life expectancy.

Summary | Cancer Is Not a Single Disease

The word “cancer” is familiar, but cancer actually includes many different diseases with different cell types, organs of origin and patterns of spread.

In Japan, approximately one in two men and women will be diagnosed with cancer during their lifetime, but the most commonly diagnosed cancers differ between men and women.

A comparison of 2023 data from Japan and New Zealand also reveals interesting similarities and differences. Prostate, breast and colorectal cancers are common in both countries, while melanoma ranks second among men and third among women in New Zealand.

Differences between countries are influenced by many factors, including population structure, lifestyle, infections, environmental exposure and genetic background. In New Zealand, UV exposure is an especially important risk factor when considering melanoma.

More broadly, cancer risk can be influenced by factors including age, tobacco, alcohol, diet, physical activity, body weight, infection, ultraviolet radiation and genetic background.

Not every cancer can be completely prevented, but understanding modifiable risk factors and taking part in appropriate screening at the recommended age can be useful parts of managing cancer risk.

When reading cancer statistics, it is also helpful to look beyond the headline number and ask “What year is the data from?”, “Is this incidence or mortality?” and “Which population does this figure describe?”.