"This is the moment it becomes malignant. Carcinoma in situ becomes invasive adenocarcinoma. The cells learn to secrete matrix metalloproteinases—molecular scissors. They cut through the collagen. They reach the submucosa. And inside the submucosa are lymphatics and blood vessels.
Now. Turn to page 342. We will go over the molecular pathways of colorectal cancer. But first—any questions?" pathology lecture
APC normally says, 'Stop dividing.' Without it, the cell becomes hyperplastic. Not cancer yet. Just... enthusiastic. A polyp. Benign. But now that cell is unstable. It divides faster than its neighbors. It acquires more mutations: KRAS (the accelerator stuck to the floor), then TP53 (the cell’s suicide switch, disabled)." "This is the moment it becomes malignant
"At this point, Margaret felt nothing. The polyp was a tiny mushroom growing in the dark. But on a colonoscopy, it would have looked like a raised red bump. If we had caught it then, we would have snip-snipped it out. Case closed. We didn't." Part 2: The Invasion (Breaking the Basement Membrane) An animation shows cells piling up, pushing through a thin blue line (the basement membrane). They cut through the collagen
A student raises a hand. "Did Margaret ever know she had cancer?"
Yesterday, I signed out her case. Let’s go back to the beginning." The slide changes. A diagram of a normal colon lining—orderly, like bricks in a wall.
"Margaret was a retired librarian. Non-smoker. Walked three miles a day. Six months ago, she noticed she felt full after eating only a few bites. She thought it was age. Three months ago, she noticed her stool was darker. She thought it was iron pills. Two weeks ago, she felt a lump in her right lower quadrant. She thought it was a muscle.