Difficulty: Intermediate | Prerequisites: Cell division, immune system basics
Cancer biology connects cell division gone wrong to the immune system's ability (or failure) to catch it. This section covers how cancers develop, how they are staged, and what risk factors drive the highest rates in the U.S. You need a basic understanding of cell division (mitosis, DNA replication) and immune system concepts (antigens, T cells, NK cells) to follow this material. Cancer is where the genetics, cell biology, and immunology units converge.
Cancer develops when cells divide uncontrollably, often aided by telomerase activity. The immune system can destroy cancer cells that display non-self antigens, but some cancers evade detection. Smoking and obesity are the two risk factors associated with the highest number of cancers in the U.S., and late-stage (stage 4) cancers that have metastasised carry the lowest survivorship.
Telomerase
An enzyme that extends telomeres (the protective caps on chromosome ends), allowing cells to divide indefinitely. Higher telomerase activity correlates with a higher likelihood of cancer (line M on a positive-correlation graph). In simple terms, telomerase gives cells a kind of immortality, which is exactly what a tumour needs to keep growing.
Cancer staging (stages 1 to 4)
A system for describing how far a cancer has spread. Stage 1 is localised; stage 4 means the cancer has metastasised to distant organs. Patients first diagnosed at stage 4 have the lowest survivorship.
Metastasis
The spread of cancer cells from the original tumour to distant organs via the blood or lymphatic system. This is what makes stage 4 cancers so dangerous.
Non-self antigens
Molecules on the surface of cancer cells that the immune system can recognise as foreign. Cancer cells that display non-self antigens are most likely to be attacked and destroyed by the immune system.
Pancreatic cancer
A cancer with high mortality rates, particularly in the southeastern United States. Its incidence is increasing, partly because of its association with obesity.
Cancer cells divide without normal controls and can invade surrounding tissues
Telomerase activity is positively correlated with cancer likelihood (line M on Fig. A: as telomerase activity increases on the X-axis, cancer likelihood increases on the Y-axis)
Normal somatic cells have limited telomerase activity, which limits their number of divisions; cancer cells reactivate telomerase to divide indefinitely
Stage 1: cancer is localised to the original site
Stage 4: cancer has spread (metastasised) to distant organs
Patients diagnosed at stage 4 have low survivorship
Early detection significantly improves outcomes
Cancer cells that display non-self antigens on their surface are most likely to be recognised and destroyed by the immune system
NK cells are part of the innate immune response against cancer, but obesity impairs their function (Fig. F: obese individuals' NK cells have higher lipid content and lower interferon production)
Some cancers evade immune detection by not displaying non-self antigens
The pair of variables associated with the highest number of cancers in the U.S. is smoking and obesity
Pancreatic cancer mortality is highest in the southeastern U.S. (Fig. D), and its incidence is increasing due to its association with obesity
Other risk factors include alcohol, environmental toxins, and lack of exercise
Line M represents a positive correlation (Y increases as X increases), used for telomerase vs. cancer likelihood
Line V represents a negative correlation (Y decreases as X increases), used for thymus size vs. age
Line Z represents a low, relatively flat relationship
Students confuse non-self antigens with non-self antibodies. The immune system recognises non-self antigens on cancer cells. Antibodies are what your immune cells produce in response.
Students often think stage 1 cancers have low survivorship. Stage 1 is localised and has higher survivorship; stage 4 (metastasised) is the one with low survivorship.
Students assume all cancer cells are detected by the immune system. Cancer cells that fail to display non-self antigens can evade immune detection entirely.
⚠️ Know how to read Fig. A: line M = positive correlation (telomerase vs. cancer), line V = negative (thymus size vs. age).
⚠️ Smoking + obesity = the pair of risk factors linked to the most cancers in the U.S. This is a commonly tested fact.
⚠️ Non-self antigens (not antibodies, not self antigens) are what make cancer cells vulnerable to immune attack.
⚠️ Pancreatic cancer: highest mortality in the southeastern U.S. (Fig. D), incidence is increasing, linked to obesity.
True or false: Stage 1 cancer has spread to distant organs. (False, that is stage 4.)
Fill in the blank: The enzyme that allows cancer cells to divide indefinitely is called ______. (Telomerase.)
True or false: Cancer cells displaying self antigens are most easily destroyed by the immune system. (False, the immune system targets non-self antigens.)
Fill in the blank: The two risk factors associated with the most cancers in the U.S. are ______ and ______. (Smoking and obesity.)
Q: Which line in Fig. A best represents the relationship between telomerase activity (X-axis) and cancer likelihood (Y-axis)?
A: Line M, because cancer likelihood increases as telomerase activity increases (positive correlation).
Q: A patient is first diagnosed with stage 4 cancer. What does this mean, and what is the prognosis?
A: Stage 4 means the cancer has metastasised (spread) to distant organs. Survivorship at this stage is low.
Q: Why are NK cells from obese individuals less effective at fighting cancer?
A: NK cells in obese individuals accumulate excess lipid, which impairs their ability to produce interferon and attack cancer cells (Fig. F).
Q: Which region of the U.S. has the highest pancreatic cancer mortality rate, and why is incidence increasing?
A: The southeastern U.S. has the highest mortality rate (Fig. D). Incidence is increasing because of the association between pancreatic cancer and obesity.
Cancer biology ties directly to the immune system material: the same NK cells, killer T cells, and antigen-recognition pathways that fight infections also patrol for cancer cells. The obesity connection links to the respiratory system notes (obesity reduces peak expiratory flow) and to the broader theme of lifestyle factors affecting health outcomes.
Cancer, tumour, neoplasm, malignant, benign, metastasis, staging, stage 4, telomerase, telomeres, non-self antigens, immune surveillance, NK cells, natural killer cells, obesity, smoking, risk factors, pancreatic cancer, survivorship, cancer mortality, BIO 118, biology 118, University of Washington