An estimated 60% of cancer patients receive chemotherapy at some point during their treatment. It’s one of the most commonly used approaches in cancer care.
We know that chemotherapy has significant limitations. It targets all cells—not just cancerous ones—which means it can also harm healthy tissues like the gut lining, hair follicles, and bone marrow. This lack of precision often leads to serious side effects and weakens the body, raising important questions about how and when it’s used.
Unfortunately, research has shown that chemotherapy can, paradoxically, create conditions that promote cancer spread, for example, by making blood vessels more permeable or awakening dormant cancer cells in distant organs. Over time, certain chemo drugs have also been linked to secondary cancers, such as leukemia, due to the DNA damage they cause in healthy cells.
A recent Chinese study (July 2025) found that chemotherapy can unintentionally reactivate dormant cancer cells in distant organs like the lungs. The researchers discovered that chemo triggers cellular senescence—a state where nearby normal cells stop dividing but start releasing inflammatory signals.
These signals, in turn, activate immune cells called neutrophils, which release web-like structures known as neutrophil extracellular traps (NETs). NETs can remodel the surrounding tissue, making it easier for dormant cancer cells to “wake up,” start dividing again, and form new tumors. This may help explain why metastasis can occur even after a tumor initially responds to treatment.
Other studies have shown that chemotherapy can damage the delicate endothelial cells that line our blood vessels. These cells play a key role in immune function, circulation, and inflammation. When these cells are disrupted, they begin releasing inflammatory compounds like IL-6 and TIMP1, which actually help cancer cells survive and thrive in the body.
Chemotherapy has been found to mobilize immature blood vessel cells, called endothelial progenitor cells, directly to the tumor site, which can further promote cancer growth and metastasis.
In lab models, chemo-treated endothelial cells become more “sticky,” making it easier for cancer cells to latch on, travel through the bloodstream, and settle into distant organs like the lungs.
In mouse models of breast cancer, researchers saw that while chemo reduced tumor size, it increased the number of cancer cells circulating through the body and forming new colonies in the lungs. The chemotherapy allows the breast cancer to penetrate through weakened junctions between blood vessels in the lungs and bind to their underlying structure, taking hold in the lungs.
Chemo also doesn’t always wipe out all cancer cells. Some survive, and those that do are often the most resistant, adaptable, and aggressive. The treatment can unintentionally select for stronger, therapy-resistant clones, which can lead to recurrence or more aggressive metastatic disease.
Some are naturally more resistant: they may grow slowly, pump the drug out, repair damage better, or have mutations that make them harder to kill. These tougher cells survive treatment and stay in the body. Over time, they can change further or take advantage of the damage chemo causes in the surrounding tissue, like inflammation or low oxygen. As a result, the tumor that grows back is often made up of stronger, more aggressive cells that are harder to treat and more likely to spread.
So what should patients do?
In some cases, chemotherapy saves lives. For fast-growing or aggressive cancers, it can be the most effective way to reduce tumor burden quickly. But it should be reserved for situations where the potential benefits clearly outweigh the risks,and ideally, it should be paired with strategies that support the body’s ability to recover and resist recurrence.
- Ask about tumor biology and alternatives. Not all cancers respond the same way to chemo. Some slow-growing tumors may not require aggressive treatment. Others may be better treated with targeted therapies or metabolic approaches. The RGCC (Greek) test exposes circulating tumor cells to chemotherapy to see which drugs are most effective, so you know which treatments may work best before starting.
- Get a second opinion. Different doctors have different approaches and may may offer more conservative options,
- Support the body’s terrain. Cancer spreads more easily in a body that’s inflamed, immunosuppressed, or hormonally imbalanced. Supporting metabolic health, thyroid function, nutrition, and stress resilience during treatment can help reduce the risk of metastasis.
So if chemotherapy can promote cancer spread in some cases, it raises serious questions about how and when it’s used. Traditionally, chemo has been the default treatment for many cancers, especially after diagnosis or surgery. But if it damages healthy tissue, awakens dormant tumor cells, or creates a microenvironment that helps cancer grow elsewhere in the body, then its use must be more carefully weighed. This doesn’t mean abandoning chemo altogether, but it does mean moving away from a one-size-fits-all approach and toward more individualized treatment plans based on tumor behavior, the patient’s biology, and the likelihood of benefit versus harm.
This also changes how we think about recurrence. When cancer returns or metastasizes after chemotherapy, it’s often viewed as a failure of the patient’s biology or the aggressiveness of the disease. But growing evidence suggests that treatment itself may unintentionally drive the emergence of more aggressive, therapy-resistant cancer clones. By killing the most vulnerable cells, chemo can leave behind resistant cells—the ones that adapt, mutate, and eventually can become more aggressive. This understanding challenges the idea that more or stronger chemo is always the answer, especially if it creates a more hostile terrain for healing.
The larger implication is that cancer care must address not just the tumor, but the entire biological and metabolic environment in which it grows. That includes supporting immune function, reducing chronic inflammation, protecting mitochondria, and maintaining healthy hormone and nutrient levels. If chemotherapy is used, it should be paired with strategies that support the body’s ability to recover and resist recurrence—such as metabolic therapies, hormone balancing, or senolytic agents that clear out damaged cells. Acknowledging chemo’s double-edged nature is a step toward smarter, more holistic cancer care.