Why Do Cancers Take Years to Develop?

 

Earlier, I wrote an article entitled:

“Our Body’s Own Natural Immunological Battle Against Cancers” here:

https://scientificlogic.blogspot.com/2024/05/our-bodys-own-natural-immunological.html

In the article, I briefly mentioned that it was found that micro cancers or cellular cancers may already be present in the body for many years before they become clinically apparent. This latency period is influenced by the slow growth of cancer cells, immune surveillance, dormancy, genetic changes over a span of several years to decades.

I mentioned the time period before micro cellular cancers lurking in the body before becoming full grown clinical cancer may take as long as 30 – 50 years, thanks to our wonderful immunological surveillance that constantly attacks these micro cancers before they grow and manifest into clinically detectable tumours. This phenomenon is well-recognized in oncology and can be attributed to several factors.

Let us now explain why micro cancers can exist for years.

First, there is a slow growth rate. Many cancer cells proliferate slowly, taking a long time to accumulate enough cells to form a detectable tumour. The tumour cells go through numerous cycles of division before they become a clinically apparent mass.

Second, the immune surveillance often recognizes and destroys abnormal cells, including early cancer cells. This keeps the growth in check for a considerable period. Some cancer cells might evade immune detection or develop mechanisms to suppress the immune response, eventually leading to a detectable tumour.

Third, there is this period of dormancy. Cancer cells can enter a dormant state where they remain inactive for years. The dormant cells can reside in niches within tissues and avoid detection and destruction.

Fourth, this is caused by genetic and epigenetic changes. Cancer development involves a series of genetic and epigenetic changes that occur over time. Early mutations might not lead to immediate aggressive growth, but additional mutations accumulated over years can trigger rapid proliferation.

Firth, this may be due to microenvironment influence. The surrounding tissue environment can suppress or support tumour growth. Factors like angiogenesis (formation of new blood vessels) are crucial for tumours expansion, and the lack of such support can delay growth.

The time frame for micro tumour development to develop into a detectable tumour varies widely depending on several reasons. Consider these factors:

First, the cancer type. Different types of cancer have different growth rates. For example, prostate cancer and certain types of breast cancer can grow very slowly, while pancreatic cancer and glioblastomas are known for their rapid progression.

Second, individual factors such as genetic predisposition, lifestyle factors (such as diet, smoking, and alcohol consumption), and overall health can influence the rate of cancer development.

Third, tumour location. Tumours in some locations may be detected earlier due to symptoms they cause, while those in others might grow larger before detection due to lack of symptoms.

Fourth, clinical detection. During the subclinical phase, cancer cells proliferate but are not yet detectable by conventional imaging or causing noticeable symptoms.

This phase can last from a few years to several decades, depending on the factors mentioned. When the tumour reaches a size where it can be detected through imaging (usually around 1 cm in diameter, containing about 1 billion cells), or starts causing symptoms, it enters the clinical phase. The transition from subclinical to clinical phase marks the point where cancer becomes detectable and typically actionable in clinical settings.

We can briefly conclude micro cancers or cellular cancers can indeed persist in the body for years before becoming clinically apparent. This latency period is influenced by the slow growth of cancer cells, immune surveillance, dormancy, genetic changes, and the influence of the tissue microenvironment. The duration before a tumour becomes noticeable can vary widely, but in many cases, it can span several years to decades.

Having explained that, then readers may ask me, what about childhood cancers? They appear early in life. What are these cancers that affect children?

Let me try to answer. Childhood cancers differ significantly from adult cancers in terms of their biology, causes, and the age at which they occur. While some cancers in adults can take years or even decades to develop, childhood cancers typically have a more rapid onset and are often linked to genetic factors rather than environmental exposures.

The common cancers affecting children are acute lymphoblastic leukaemia (ALL): accounting for about 25-30% of all childhood cancers. Then we also have acute myeloid leukaemia (AML) that is less common than ALL but still a significant type of childhood leukaemia. Interestingly, the common flowery plant called Catharanthus roseus (Madagascar periwinkle) has been found to be effective against leukaemia. 

The plant is exploited and studied as a medicinal plant as it was found to produce more than 100 monoterpenoid indole alkaloids that contain the two major vital cytotoxic dimeric alkaloids that are used for cancer chemotherapy treatment, also many alkaloids have a medicinal role. The compounds include the anti-cancer compounds: Vinblastine and Vincristine (Magnotta, 2006).  The alkaloid vincristine has a role for treating leukaemia in children.

Also consider brain and central nervous system (CNS) tumours such as medulloblastoma that is the most common malignant brain tumour in children.

Following that are the gliomas including astrocytomas, ependymomas, and brain stem gliomas.

Then there are the ependymomas that arise from the ependymal cells lining the ventricles of the brain and the central canal of the spinal cord. Childhood cancers affecting the CNS may also be the neuroblastoma that arises from immature nerve cells and primarily affects infants and young children, usually under the age of 5.

Others are Wilms tumour (Nephroblastoma), a kidney cancer that primarily affects children, most commonly between the ages of 3 and 4.

We also have those lymphomas that include Hodgkin lymphoma, more common in adolescents and the non-Hodgkin lymphoma that includes various subtypes, such as Burkitt lymphoma, lymphoblastic lymphoma, and large cell lymphoma.

Other cancers affecting children are also the rhabdomyosarcoma, a cancer of soft tissue, such as muscle, and can occur in many places in the body, the retinoblastoma, a cancer of the retina, typically affecting children under the age of 5.

Children may also suffer from bone cancers. They include osteosarcoma, the most common bone cancer in children, usually occurring in the long bones of the arms and legs. Besides that, we have the Ewing sarcoma, which is another type of bone cancer, which can also occur in soft tissue.

Then, we go back to this question we asked. Why childhood cancers occur early when I said cancers may take decades to develop? Quite honestly, I cannot give you the definitive answer to that question.  

However, here are some of the influencing factors we can consider.

Genetic predisposition among newborns. Many childhood cancers are linked to genetic mutations that occur early in life, either inherited or occurring in utero. Conditions like Down syndrome and genetic syndromes such as Li-Fraumeni, Beckwith-Wiedemann, and neurofibromatosis increase the risk of certain childhood cancers.

We can also consider developmental factors such as during childhood, cells are rapidly dividing and differentiating, which can lead to a higher likelihood of errors in cell division, resulting in cancer. Embryonal cells that are supposed to mature into specific tissues may give rise to tumours if they remain immature and proliferate abnormally.

Perhaps scientists and medical researchers like me may also like to consider environmental factors although less common. We believe certain environmental exposures such as radiation or maternal smoking during pregnancy can increase the risk of childhood cancers.

I think we may summarize the reasons why childhood cancers typically appear early in life are because of genetic mutations, developmental factors, and occasionally environmental exposures. They tend to develop rapidly compared to many adult cancers.

The most common childhood cancers once again include leukaemia, brain and CNS tumours, neuroblastoma, Wilms tumour, lymphomas, rhabdomyosarcoma, retinoblastoma, and bone cancers like osteosarcoma and Ewing sarcoma. These cancers often present unique challenges and require specialized treatment approaches tailored to young patients.

I hope this satisfies other medical scientists, researchers and the clinicians, especially paediatric oncologists.

Lim ju boo