Immunotherapy...what is that?

You can't google "cancer treatment" without seeing the word "immunotherapy" these days. Well, let me break it down for you.

Chemotherapy: drugs that damage all dividing cells

Immunotherapy: drugs/treatments that cause the immune system to attack (cancer) cells

Cancer is the crime syndicate

Cancer is made of ordinary cells of the body that turn to a life of exploitation of the normal cells around them. This happens because of environment, genetic disposition, or other factors we can't quite get a handle on. This isn't the body's fault, it just happens. The cancer invades other organs and exploits space and nutrients.

The cancer/crime syndicate creates a legitimate front

The cancer cell doesn't want to die. It "thinks" it is not doing anything wrong. They look like normal cells of the body and this is what make them hard to target without taking out some innocent bystanders. However, scientists are figuring this out. One thing they found is that cancer cells can display a molecule on their surface that tells the immune system not to kill it. This is PD-L1. Other cancer cells over-express molecules such as Her2 or CD19 that we can train elite killers to sneak in and target.

"Chemotherapy" is a bomb

Chemotherapy -- referred to by oncologists as "cytotoxic" chemotherapy -- kills cells mainly by messing up their ability to copy themselves. Most cells in the body have to make copies of themselves...so this kind of therapy doesn't really distinguish between cancer and not cancer. Why doesn't it kill you? Because usually, the cancer is dividing faster and so more cancer cells will die than body cells and over time (a long time) researchers figured out the balance between killing the cancer and killing you. So basically, back to my analogy: if cancer is an enemy, chemotherapy is like setting off a bomb. Yeah, you'll demolish your enemy (though not all of them) but you'll hurt innocent bystanders as well. This used to be the only weapon we had, so that collateral damage was acceptable. But we can do better.

PD-1 and PD-L1 Blockers: Taking away the front

So the crime syndicate has set up a legitimate front where it can launder money and look like the rest of the cells of the body despite the fact that behind it all, they are invading territory and stealing community resources. Sometimes it even damages and kills surrounding normal hard working cells. However, we can take that front away and expose the cancer cell as the renegade it is. We do this with antibodies or "blockers" to PD-1 (on the immune cells) or PD-L1 (on the cancer). Scientifically, what is really happening is that PD-1 and PD-L1 see each other and create a "no kill" signal. We merely stop them from seeing each other, and the cancer cell is destroyed.

Not Perfect: Some normal cells rely on this, too

Sorry to say, this blockade is not perfect. Some normal cells rely on the PD-1 / PD-L1 reaction to keep the immune cells from attacking them. We don't fully understand it, but some (not all) patients can develop attacks on their lungs, skin, intestines, thyroid, and other organs (thank goodness, hardly ever at the same time, if at all) and these tissues can be damaged.

Other kinds of immune therapies

So the PD-1 antibodies and PD-L1 antibodies are the main ones being advertised right now. However, there are other ways to make the immune system attack the body. For a while now, medical scientists have been finding ways to take white cells (the cells that fight off invaders) out of the body, "train" them to attack cells with a specific quality -- say CD19 on B cells or PSAP on prostate cancer cells. This is the premise behind CAR-T cells.

Not cure-all miracles

The problem with these is that despite all the hype, they still don't get rid of cancer forever if it has spread to other organs. The surviving criminals figure out what's going on and they learn to avoid the traps that brought down the others. The grow and spread and resist. Still, I think about how far we've come, and the incredible minds behind the bench working on new treatments every day and I have hope. We're coming for you, cancer.

Thanks for reading.

-Dr G.