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Cancer Biology
Hallmarks of Cancer
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Cancer develops when normal cells acquire traits that let them grow, survive, and spread despite the body's control systems. These shared traits are called the hallmarks of cancer, and they help explain how many different cancers behave in similar ways. Learning the hallmarks gives students a framework for linking molecular changes to tumor growth, invasion, and treatment response. It also connects basic cell biology to pathology, pharmacology, and clinical oncology.
The hallmarks arise through mutations, epigenetic changes, and altered signaling between tumor cells and their environment. Cancer cells often activate growth pathways, ignore anti growth signals, resist cell death, and gain the ability to replicate indefinitely. As tumors progress, they also stimulate blood vessel formation, evade immune attack, reprogram metabolism, and invade distant tissues. These mechanisms are not isolated, because each hallmark can support the others during cancer progression.
Key Facts
- Self sufficiency in growth signaling often involves oncogene activation such as RAS, MYC, or EGFR.
- Insensitivity to anti growth signals commonly reflects loss of tumor suppressors such as RB or TP53.
- Resistance to apoptosis can occur through increased BCL 2 activity or loss of p53 mediated cell death pathways.
- Replicative immortality is linked to telomerase reactivation, which maintains telomere length during repeated division.
- Tumor angiogenesis is driven by factors such as VEGF that promote new blood vessel growth when oxygen is limited.
- Warburg effect: many cancer cells favor glycolysis even with oxygen present, so glucose -> lactate despite aerobic conditions.
Vocabulary
- Oncogene
- An oncogene is a mutated or overactive gene that pushes cells toward uncontrolled growth and division.
- Tumor suppressor gene
- A tumor suppressor gene normally slows cell division, repairs damage, or triggers cell death when needed.
- Apoptosis
- Apoptosis is a programmed cell death process that removes damaged or unnecessary cells in an orderly way.
- Angiogenesis
- Angiogenesis is the formation of new blood vessels that can supply a growing tumor with oxygen and nutrients.
- Metastasis
- Metastasis is the spread of cancer cells from the original site to distant organs where new tumors form.
Common Mistakes to Avoid
- Thinking every cancer shows every hallmark in the same way, which is wrong because different tumors reach these traits through different genes and pathways.
- Confusing oncogenes with tumor suppressor genes, which is wrong because oncogenes are activated to drive growth while tumor suppressor genes usually promote cancer when they are lost or inactivated.
- Assuming benign tumors are metastatic, which is wrong because metastasis is a defining feature of malignant cancer, not benign growths.
- Treating angiogenesis as the same as invasion, which is wrong because angiogenesis builds blood supply while invasion is the movement of cancer cells into surrounding tissue.
Practice Questions
- 1 A tumor cell line doubles from 2.0 x 10^5 cells to 1.6 x 10^6 cells. How many cell doublings occurred?
- 2 A researcher measures telomere length in a cancer cell population. If the average telomere length would shorten by 50 base pairs per division without telomerase, how many base pairs would be lost after 20 divisions?
- 3 A biopsy shows high VEGF expression, reduced apoptosis, and loss of E cadherin. Explain which hallmarks of cancer these findings support and how they could make the tumor more dangerous.