Cancer 102

In Cancer 101, I gave some basics to understanding cancer. A commenter asked a good question, and our next lesson will attempt a simple answer.

The question regarded how a pathologist can tell if a cancer is “invasive” by looking at a specimen. Well, depending on the specimen, the answer changes, but let’s use the colon as an example. Most colon cancers start out as benign polyps. Eventually the cells in the polyp can become malignant, and after that, they can they can begin to grow through layers of normal cells.

Here is a diagram of a cancer of the colon at various stages. As you can see, at a certain point, the cancer begins to grow through each layer. The ability to grow through, or invade, other layers is one of the things that makes cancers behave in a nasty manner.

i-879e97c9f33a541f1465fb682da71e1e-cancermicro.jpgHere is a piece of colon cancer under the microscope. This could have been from a biopsy of a polyp, or from a tumor completely removed by a surgeon. The stripe of light purple cells labeled “normal muscle layer” should extend across uninterrupted. Instead, a glob of darker purple cells is growing through the muscle layer, destroying it. Once the cancer cells get to a blood vessel, they can go anywhere in the body (metastasize). That’s bad.

I hope that’s helpful.


  1. T. Bruce McNeely

    A couple of quibbles from a pathologist:
    1) That specimen is a surgical resection. A biopsy would be smaller, and would include mucosa, and sometimes muscularis mucosa and submucosa. If you’ve got muscularis propria and serosal fat in your endoscopic biopsy, you’re in deep doo-doo (pun intended).
    2) Assessment of invasion also includes identification of tissue destruction by the tumor, as well as assessment of whether the basement membrane has been breached. An in situ tumor can extend into deeper layers without invading, if it tracks down into deep glands or pushes downward without penetrating the basement membrane. This is not considered invasion. However, your explantion is essentially correct.

  2. Thank…my science-y posts usually have a disclaimer re oversimplification at the beginning, but i fergot it this time.

    Yes, this one is clearly surgical…

    But as you said, i think it gets the basic point across to non-path folks…

    i hope

  3. Steven Chang

    Treat Cancer with Flavonoids!

    [ed note…i took the url out of this to avoid click throughs. It goes to one of those “vitamin c cures cancer” sites, which you can feel free to google]

  4. well, i’m not deleting chang’s crazy-ass bullshit, because it’s going to need a good fisking, and reporting it to the ftc/fda might be a useful thing to do.

  5. Just popping in to say that this and its predecessor are excellent posts! Nicely explained and at a level that should be accessible to many

    *says she who used to write about the nitty gritty details for aberrant DNA methylation in colon and prostate cancers and the catalytic mechanism of matrix metalloproteases and now writes informed consent forms at an eighth grade reading level for cancer patients entering trials*

  6. Wow! a post in reply, with pictures. Thanks.

  7. Andy harris

    I really appreciate this post and the one preceding it. I’m not in any medical field and you demystified cancer for me is a short direct explanation. I feel like you gave me a solid gist of something that everyone talks about but few actually firmly grasp. You have a knack for taking the complex and making it accessible to the rest of us. Keep it up!

  8. Andy Harris

    You SHOULD delete Steve “spamming” Chang post from your blog. I don’t know jack about medicine but I do know about online marketing. He is attempting to use your blog to build links to his snake oil website. More spammy links like this will equal more traffic from all the minor search engines that still include blog comment links as part of their ranking system.

    DELETE his post

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