Testicular germ cell tumour is a type of cancer that develops from the cells in the testicles responsible for making sperm. While it remains a rare form of cancer overall, it stands out as the most common cancer affecting young men, particularly those between the ages of 15 and 35. Despite its occurrence in a younger population, this cancer has become a success story in modern medicine, with very high cure rates when detected and treated properly.

Understanding the Numbers: Who Gets Testicular Germ Cell Tumours

Testicular germ cell tumours represent more than 90% of all testicular cancers, making them the dominant type when cancer affects the testicles. Though the disease is rare in the general population, affecting roughly 1 in 250 men during their lifetime, the incidence has been steadily rising in many countries, including the United States and across Europe.^[1][4]

The pattern of who develops this cancer reveals important age-related trends. While testicular cancer can occur at any age, from infancy through old age, certain age groups face higher risk. Young adults are most commonly affected, with the highest incidence occurring between ages 15 and 35. In the United States, about 8,000 men were estimated to be diagnosed with testicular germ cell cancer in 2013, with approximately 370 predicted to die from the disease.^[4]

Germ cell tumours in children are relatively rare, making up only 3.5% of cancer diagnoses in this age group. However, as children reach adolescence and young adulthood, the rates climb significantly. Among those aged 15 to 19, germ cell tumours account for 13.9% of all cancers diagnosed, highlighting the particular vulnerability of this age bracket.^[1]

One notable demographic pattern involves ethnicity. Men who are Caucasian face a greater risk of developing testicular cancer compared to men of other ethnic backgrounds. This disparity in incidence rates suggests that both genetic and possibly environmental factors play roles in who develops the disease.^[4]

When examining data from the United States between 2001 and 2020, seminomas—one of the two main types of testicular germ cell tumours—accounted for 54% of all testicular cancers diagnosed. The distribution shows that seminomas are particularly common in men aged 30 to 44, where they represent 63.6% of testicular cancer cases. In older men aged 45 to 64, the proportion rises even higher to 73.2%.^[4]

What Causes This Cancer to Develop

The exact reasons why testicular germ cell tumours form remain unclear, but researchers have identified several important factors in the disease’s development. These tumours originate from germ cells, which are the reproductive cells that in males eventually mature into sperm. The word “germ” in this context is short for “germinate,” which means to mature, and has nothing to do with germs or infections.^[1]

Scientists believe that testicular germ cell tumours develop from a pre-cancerous condition called germ cell neoplasia in situ (GCNIS), sometimes referred to as intratubular germ cell neoplasia. This condition involves abnormal cells that exist only within the tiny tubes inside the testicle where sperm production occurs. At this stage, the cells look abnormal under a microscope but haven’t yet spread beyond these tubes. GCNIS itself doesn’t cause symptoms and isn’t yet cancer, but it can progress to become invasive cancer. About 50 out of 100 men with GCNIS will develop cancer within five years.^[5]

The development of GCNIS is thought to occur when normal maturation of certain cells called gonocytes fails during fetal development or shortly after birth. These immature cells persist and can later, typically after puberty, transform into cancerous tumours. This explains why most testicular germ cell tumours appear in adolescents and young adults rather than in children.^[6]

Unlike many other cancers, testicular germ cell tumours have a very low rate of point mutations—changes in individual building blocks of DNA. Instead, nearly all of these tumours show gains of genetic material on chromosome arm 12p and have abnormal numbers of chromosomes overall, a condition called aneuploidy. These genetic characteristics help distinguish testicular germ cell tumours from other types of cancer.^[6]

Both inherited genetic factors and environmental exposures appear to contribute to the risk of developing testicular germ cell tumours, though no single cause has been identified. The rising incidence rates over recent decades suggest that environmental or lifestyle factors may be playing an increasingly important role, though the specific factors remain under investigation.^[6]

Who Faces Higher Risk

Several well-established risk factors increase the likelihood that someone will develop testicular germ cell tumours. Understanding these risk factors can help identify who might benefit from increased awareness and self-examination, though having risk factors doesn’t mean cancer will definitely develop.

One of the strongest risk factors is having an undescended testicle, medically known as cryptorchidism. Normally, testicles form inside the abdomen during fetal development and descend into the scrotum before or shortly after birth. When one or both testicles fail to descend, the risk of developing testicular cancer increases. Surgical correction of an undescended testicle before puberty may lower this risk, though this remains uncertain.^[4][10]

Family history represents another significant risk factor. Men who have a father or brother who has had testicular cancer face a greater risk of developing the disease themselves. This familial clustering suggests that inherited genetic factors contribute to susceptibility. Researchers have identified more than 30 genetic regions associated with increased testicular germ cell tumour risk, indicating that many genes, each with a small effect, combine to influence overall risk.^[4][6]

A personal history of testicular cancer in one testicle significantly increases the risk of developing cancer in the other testicle. While only 1 to 3% of men with testicular cancer develop cancer in both testicles, those who have already had the disease once need ongoing monitoring. Additionally, the cancer-free testicle may not function normally in some men who have had testicular cancer.^[4][18]

Having abnormally developed testicles also increases risk. This includes various conditions that affect testicular development or structure. Age itself acts as a risk factor, with young adults facing the highest risk, though the specific type of testicular germ cell tumour varies by age group.^[4]

Recognizing the Warning Signs

Symptoms of testicular germ cell tumours depend largely on where the tumour develops and whether it has spread beyond the testicle. Many men first notice something is wrong when they discover a change during routine bathing or dressing, which is why knowing what’s normal for your body is important.

The most common symptom is a firm lump or painless mass on the testicle. This lump typically feels different from the normal tissue of the testicle and may be discovered accidentally rather than causing any discomfort. The discovery of any new lump or swelling in the testicle should prompt a medical evaluation, as testicular cancer is highly treatable when caught early.^[3][20]

Men may also experience swelling of the testicle or scrotum without a distinct lump. This swelling might develop gradually or appear suddenly. Some men report a feeling of heaviness in the scrotum, testicles, or the area between the scrotum and anus called the perineum. This sensation of heaviness can feel like a constant, uncomfortable weight.^[1]

While many testicular germ cell tumours are painless, some men experience a dull ache in the testicles, scrotum, or lower abdomen. This ache differs from sharp, sudden pain and tends to persist rather than come and go. Rarely, men may experience sudden, sharp pain in or around the testicles, though this is less common.^[1]

In some cases, men notice blood in their semen, a condition called hematospermia. While this symptom can have other causes, it warrants medical attention to rule out serious conditions including cancer.^[1]

If the cancer has spread beyond the testicle, additional symptoms may develop depending on where it has spread. Spread to lymph nodes in the neck can cause visible or palpable lumps. If cancer spreads to the lungs, symptoms might include persistent cough, shortness of breath, or chest pain. Spread to the abdomen can cause back pain, while spread to other areas might cause symptoms specific to those locations, such as bone pain if it reaches the bones.^[1]

It’s important to note that symptoms often occur because a growing tumour puts pressure on nearby tissue or organs. For example, a testicular germ cell tumour can cause swelling or pain in the scrotum as it enlarges. Understanding that symptoms may be subtle or easily dismissed makes regular self-examination even more important.^[3]

Steps to Lower Your Risk

Unlike some cancers where clear prevention strategies exist, preventing testicular germ cell tumours remains challenging because many risk factors cannot be changed. However, certain steps may help reduce risk or ensure early detection, which significantly improves treatment outcomes.

For parents of boys with undescended testicles, seeking surgical correction called orchiopexy before puberty appears to potentially lower the risk of testicular cancer, though research hasn’t definitively confirmed this protective effect. Regardless of whether risk is reduced, surgical correction addresses other health concerns related to undescended testicles and allows for easier monitoring later in life.^[10]

Regular self-examination represents the most important step men can take. By becoming familiar with how their testicles normally feel, men can quickly identify any changes that might indicate a problem. Self-examination should be performed monthly, ideally during or after a warm bath or shower when the scrotal skin is relaxed. Men should gently roll each testicle between their thumb and fingers, feeling for any lumps, changes in size, or areas of pain. Knowing your normal is key to recognizing when something changes.^[20]

While self-examination doesn’t prevent cancer, it enables early detection, which is crucial because testicular germ cell tumours are highly curable when caught early. Men with risk factors—such as a personal or family history of testicular cancer, undescended testicles, or abnormally developed testicles—should be particularly vigilant about self-examination and should discuss appropriate monitoring schedules with their healthcare providers.

Unlike some other cancers, there are no specific lifestyle modifications, dietary changes, or supplements that have been proven to prevent testicular germ cell tumours. The genetic and developmental nature of the disease means that traditional prevention strategies focused on behavior change have limited applicability.

Awareness and education play crucial roles. Young men, particularly those in high-risk age groups or with risk factors, should be educated about testicular cancer, its symptoms, and the importance of self-examination. Healthcare providers should discuss these topics during routine examinations, especially with adolescents and young adults.

For men who have already been treated for testicular cancer in one testicle, regular monitoring of the remaining testicle is essential. While fertility may be affected—some research indicates that fertility can be poor for up to two years before testicular cancer is discovered—understanding these risks and discussing fertility preservation options before treatment can help men make informed decisions about their reproductive future.^[18]

How the Disease Changes Normal Body Function

Understanding how testicular germ cell tumours affect normal bodily processes helps explain why symptoms develop and why treatment must address multiple aspects of health. The pathophysiology—the changes in normal function caused by disease—of testicular germ cell tumours involves both the physical presence of the tumour and the biological changes it creates.

Normal testicles serve two main functions: producing sperm for reproduction and manufacturing hormones, particularly testosterone, which regulates male sexual characteristics, muscle mass, bone density, and various other bodily functions. When a germ cell tumour develops, it interferes with both these functions, though the degree of interference varies depending on tumour size, location, and type.

The tumour itself physically occupies space within the testicle. As it grows, it can distort normal testicular architecture and compress healthy tissue. This mechanical effect explains why men often feel a lump or experience swelling. The growing mass stretches the capsule surrounding the testicle and can create the sensation of heaviness or aching that some men experience.

Certain types of testicular germ cell tumours produce substances that can be measured in the blood, called tumour markers. Three important tumour markers are alpha-fetoprotein (AFP), beta-human chorionic gonadotropin (beta-hCG), and lactate dehydrogenase (LDH). Non-seminomas often produce elevated levels of AFP and beta-hCG, while seminomas may produce elevated beta-hCG but never produce AFP. These markers are crucial for diagnosis, monitoring treatment response, and detecting recurrence. The production of these abnormal proteins represents a biochemical change from normal testicular function.^[10]

The presence of cancer can trigger immune responses. Some seminomas, particularly certain subtypes, show evidence of immune cell infiltration, where the body’s immune system responds to the tumour’s presence. This immune response represents the body’s attempt to fight the cancer, though it’s typically insufficient to eliminate the tumour without treatment.^[4]

If the cancer spreads beyond the testicle, it typically follows predictable pathways. It often first spreads to nearby lymph nodes in the back of the abdomen, called retroperitoneal lymph nodes. From there, it may spread to lymph nodes in the chest or directly to organs like the lungs, liver, or brain. This spread pattern reflects how cancer cells break away from the original tumour, enter the lymphatic system or bloodstream, and establish new tumours in distant locations. This process, called metastasis, represents a fundamental change in how cancer affects the body, as it now involves multiple organ systems rather than just the testicle.^[10]

Advanced testicular germ cell tumours can affect organs where they spread. Lung involvement might impair breathing by occupying space in the chest or causing fluid accumulation. Lymph node involvement in the abdomen can press on other structures, potentially affecting digestion or kidney function. These secondary effects demonstrate how cancer changes normal physiology not just at the primary site but throughout the body if left untreated.

Interestingly, testicular germ cell tumours show extensive aneuploidy—abnormal numbers of chromosomes—but surprisingly low rates of gene mutations compared to many other cancers. This genetic characteristic suggests that the mechanisms driving these tumours differ from those in cancers that accumulate many mutations over time. The near-universal presence of extra copies of genetic material from chromosome 12p appears particularly important in the disease’s development.^[6]

The biochemical environment within the tumour also changes. Cancer cells often have altered metabolism, growing rapidly and consuming large amounts of nutrients. This altered metabolism can be detected through imaging tests that show areas of high metabolic activity. Additionally, the unique sensitivity of testicular germ cell tumours to platinum-based chemotherapy reflects underlying cellular characteristics, including how these tumours respond to DNA damage and whether they can repair such damage or undergo cell death in response to treatment.^[11]