Cancer becomes far more dangerous when it spreads beyond its original site. Some cancers stay in one place, while others travel through the body, settling in new areas and making treatment much harder. It is this process, known as metastasis, that makes cancer so deadly. But why does this happen? Cancer cells are survival experts. They adapt, hide, and move through the body, forming new tumours without being caught.
We spoke to Dr Govind Eriat, Consultant- Hematology and BMT Medicine, Gleneagles BGS Hospital, Kengeri, Bengaluru, who explained why some cancers metastasise rapidly while others remain localised.
How Cancer Cells Escape and Spread
Each cancer cell in a tumour is a copy of the first cancer cell that escaped surveillance and became immortal. “The spread of cancer, known as metastasis, is the main reason why cancer is often fatal. The invading tumour cell, on its way to the target site, interacts with other proteins and cells to overcome the host at all odds. It's like an invasion, where the cancer cells fight to take control, and the outcomes can be devastating,” explained Dr Eriat.
Why Some Cancers Spread While Others Don’t
Different types of cancer behave differently because they originate from distinct tissues. The way kidney cancer spreads is not the same as breast cancer. Each organ comes from a different embryonic layer, meaning the mechanisms that drive cancer growth and metastasis vary. Cancer stem cells, which act like fugitives, escape immune surveillance and repair mechanisms, lying dormant until the right moment to strike again.
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The Role of Genetic and Environmental Factors
“Cancer can develop when genetic disruptions combine with environmental triggers. These triggers can include ageing, disrupted sleep patterns, and physical pressures that affect the tissue around cells,” explained Dr Eriat.
Poor cell-cell interactions, including a lack or excess of soluble signals, such as growth factors and cytokines, can create a perfect storm for cancer cells to spread, especially in the presence of intratumoral microbiota, as reported by Fares et al. in Nature magazine.
How Cancer Cells Travel Through the Body
Cancer cells can travel through the body by breaking down the walls of blood vessels and lymph nodes. They can also hide from the immune system to avoid being detected.
For cancer cells to spread, a group of cells must work together to invade new tissues. This process is called Epithelial-Mesenchymal Transition (EMT). During EMT, cancer cells change and become more aggressive, allowing them to spread to new body parts.
A transdifferentiation process occurs, through which transformed epithelial cells develop the ability to invade, resist stress, and disseminate. The metastatic sequence can be conceptualised as detachment from the primary tumour, followed by invasion, intravasation into a vessel, circulation, stasis within a vessel, extravasation, invasion of the recipient tissue bed, and ultimately proliferation.
“Certain signals in the body can help cancer cells spread. The tumour microenvironment, which comprises all surrounding cells, extracellular matrix, and immune cells within the tumour microenvironment, can significantly influence metastasis by providing cues for invasion, angiogenesis, and cell survival,” added Dr Eriat.
Key Pathways That Drive Metastasis
Specific signalling pathways play a major role in metastasis, depending on the cancer type:
- Breast cancer often metastasises to the bone through the activation of specific signalling pathways, such as the receptor activator of the nuclear factor-κB (RANK) pathway, which leads to bone resorption and tumour cell colonisation.
- Prostate cancer frequently metastasises to the bone due to the expression of androgen receptors, which are targeted by therapies to inhibit metastasis.
- Melanoma can spread widely through the bloodstream due to its high migratory and invasive capabilities, often associated with the Mitogen-Activated Protein Kinase (MAPK) activation pathway.
- For blood-related cancers, movement to any part of the body is relatively easy, leading to rapid growth and sudden symptoms, with quick progression if left untreated.
[Disclaimer: This article contains information provided by an expert and is for informational purposes only. Hence, we advise you to consult your professional if you are dealing with any health issue to avoid complications.]