← Biology Classroom Tools Bio Tool #19 · Biology I Unit 2 · SOL BIO.3 · PWCS LT 2.3

The Cancer Pathway: How One Cell Breaks Away

Running on
  1. Healthy tissue. Healthy cells listen to their neighbors. They divide only when the tissue needs new cells, stop when it is full, and stay attached in their own tissue.
  2. Damage to the instructions. Sunburns, tobacco smoke and other causes can damage the instructions stored in a cell's nucleus. Most damage is repaired, or the damaged cell dies.
  3. One cell stops listening. Now and then a damaged cell keeps dividing when its neighbors signal stop. Every new cell inherits the same broken instructions.
  4. A tumor forms. The extra cells pile into a lump called a tumor. It crowds healthy cells and takes their space and food, and the tissue can no longer do its job. Homeostasis slips.
  5. A new blood supply. A growing tumor needs oxygen and sugar like every cell. It sends signals that make new blood vessels grow into it.
  6. Breaking through. Some cells let go of the cells around them and push through the thin layer under the tissue. Now the tumor is invading. A tumor that does this is malignant.
  7. Riding the bloodstream. A few cells slip into a blood vessel and ride the bloodstream. Most die on the trip. A few survive.
  8. A new organ. One survivor leaves the blood in a new organ and starts dividing again. Spreading to a new place is called metastasis. Now more than one organ, and more than one organ system, is in trouble.
  9. Catching cancer early matters. For melanoma found before it spreads, more than 99 out of 100 people are alive five years later. Once it has spread to distant organs, about 36 out of 100 are. Source: American Cancer Society.

One skin cell stops listening to its neighbors. Follow its descendants from a lump in the skin, through the bloodstream, to a second tumor in the lung.

It plays by itself and loops, about a minute and a half each time round. There is nothing to answer. Pause holds any stage for talking; Projector makes the words bigger and holds each stage longer. The cells and vessels are drawings, not to scale.

For teachers

Where students are

In Unit 2 students know the cell, the nucleus as the place the DNA is kept, the cell membrane, organelles, the levels of organization from cell to organism, and homeostasis. They have not met DNA structure, the cell cycle, mitosis or the immune system. The story uses only what they have, and each stage carries a chip naming the unit where the rest comes back.

The eight stages

  1. Healthy tissue
  2. Damage to the instructions
  3. One cell stops listening
  4. A tumor forms
  5. A new blood supply
  6. Breaking through
  7. Riding the bloodstream
  8. A new organ

Where it comes back

  • Unit 3, Cell Energetics: why a tumor needs its own blood supply of sugar and oxygen.
  • Unit 4, Nucleic Acids & Protein Synthesis: what “damage to the instructions” means, and how a change in the DNA changes the message.
  • Unit 5, Cell Growth, Division & Specialization: the controls on dividing that the rogue cell ignores.

Choices in the drawing

  • The cell that goes wrong carries dark pigment granules from the first frame. It is a pigment cell, because melanoma, the cancer in the closing numbers, starts in pigment cells; the second tumor is still melanoma, not lung cancer.
  • Most damage is repaired or the damaged cell dies, and stage 2 shows both before one cell keeps its damage, so students do not leave thinking every sunburn becomes cancer.
  • Benign and malignant are separated once, at stage 6: a tumor that crosses the thin layer under the tissue is malignant.
  • The rogue cells differ by shape as well as color (round, with a lumpy nucleus), so the difference holds in grayscale and for color-blind viewers.
  • Five cells enter the blood and one arrives; the counter at the top of stage 7 keeps score.

In class

Project it with Projector on, or link to cancer-pathway.html?projector=1 to open that way. Pause on a stage to ask what students already know about it. Students can rewatch from Canvas; nothing is collected, and the only things this device remembers are the Projector and Running on settings.