how does cancer not always relapse after radiation treatment

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Cells are tiny and there are billions upon billions of then in our body. If cancer starts to form, how is it that in some cases, treatment can kill every single cell and cure a person of cancer? Isn’t leaving even one cancerous cell dangerous as it’ll multiply infinitely?

In: Biology

The cells in your body are constantly winning wars vs cancer cells. Your body sees cancer cell mutation as foreign and destroys them before they spread. Sometimes some slip through and multiply, in which can spread to parts of the body and start taking over. Radiation helps destroy cancer cells (and normal cells) so eventually the balance can be maintained again.

First point is that the human body has an amazing capacity to fight off things it considers foreign and that includes cancer. However with cancer, (as you say) the body sometimes cannot fight it off fast enough to stop it from spreading. Treatments for cancers are a means to slow down the cancerous growth, kill some of the cancer cells to the point where the immune system can take care of the rest. (simplistically put)

Many of the incurable diseases today are auto-immune disorders. This is where our own bodies go haywire on us and things that should not happen, do happen and the body does not recognize it as “wrong”. Without the body’s self repair system working, these kind of disorders are often chronic, progressive and ultimately fatal.

Not all cancer cells are equal. If the radiation kills the most “cancerous” of the cancer cells, the rest of the tumor can be destroyed by the body.

Heterogeneity is the technical terminology for this.

You are right that all it takes is a single cancer cell for the cancer to relapse.

So when we give radiotherapy we definitely want to kill every single cell, otherwise the treatment will have been in vain.

To tackle this, we do two things

1) Deliver high enough doses to statistically kill every cell in the irradiated area with high certainty.

2) Deliver dose to a small volume surrounding the tumor to have some margin and account for cells which possibly have detached from the gross tumor.