Cancer
When checkpoints, cyclins or proteins such as p53 stop working, a cell can divide without the usual restrictions. If it also escapes surveillance by the immune system, the result is a population of cells that grows out of control: a tumor. Understanding cancer as a disease of the cell cycle explains its origin, its treatments and its prevention all at once. Picture a dermatologist at a school sports physical who spots a mole that has changed shape and color: is it a harmless spot or the first sign of melanoma? By the end of this page you will know how to reason about that question.
What cancer is: uncontrolled proliferation
When you cut your skin, cells proliferate until the edges meet and contact inhibition stops the division; in a neoplasm, however, the cells keep multiplying, piling up and invading neighboring tissues without heeding any stop signal: what has gone wrong in the cell's internal program for it to ignore the limits of its own tissue?
What is cancer? Explain its relationship with cell cycle alteration.
What is cancer? Explain its relationship with cell cycle alteration.
Distinguish between a benign tumor and a malignant tumor, and explain what metastasis is.
Distinguish between a benign tumor and a malignant tumor, and explain what metastasis is.
Proto-oncogenes and tumor suppressor genes
The diagram compares the role of two types of genes in controlling cell division, in their normal form and when mutated. Explain which type of gene (proto-oncogene or…
The diagram compares the role of two types of genes in controlling cell division, in their normal form and when mutated. Explain which type of gene (proto-oncogene or tumor suppressor gene) corresponds to A and B, which kind of mutation (activating or inactivating) alters it in each case, and how each contributes to the onset of cancer.
Carcinogens, viruses and the origin of mutations
In 1964 the US Surgeon General concluded that cigarette smoking causes lung cancer, and a similar pattern shows up today in people who get repeated sunburns at the beach or on a baseball field: through what common mechanism do physical, chemical and biological agents as different as these manage to transform a healthy cell into a cancerous one?
Tobacco is responsible for most lung cancers. Explain what a carcinogen (or carcinogenic agent) is and give two more examples of carcinogens other than tobacco, stating…
Tobacco is responsible for most lung cancers. Explain what a carcinogen (or carcinogenic agent) is and give two more examples of carcinogens other than tobacco, stating the type of cancer they promote.
Human papillomavirus (HPV) can cause cervical cancer. Explain how a virus can induce cancerous transformation of a cell and what effective preventive measure exists…
Human papillomavirus (HPV) can cause cervical cancer. Explain how a virus can induce cancerous transformation of a cell and what effective preventive measure exists against HPV.
Angiogenesis and chemotherapy
A chemotherapy drug acts by inhibiting the depolymerization of the spindle apparatus during the M phase, which blocks the spindle assembly checkpoint and induces…
A chemotherapy drug acts by inhibiting the depolymerization of the spindle apparatus during the M phase, which blocks the spindle assembly checkpoint and induces programmed cell death.
- a) Justify at the molecular and tissue levels why this drug causes acute side effects such as neutropenia, anemia, alopecia, and gastrointestinal mucosal lesions, whereas striated muscle tissue and nervous tissue experience almost no immediate toxicity.
- b) A solid tumor has a growth fraction (percentage of cells actively dividing versus cells in G0 phase) of only 10%, while the remaining 90% is in quiescence. Predict and justify the efficacy of this chemotherapy agent against this tumor, and explain the risk posed by G0 cells re-entering the cell cycle after treatment ends.
Analyze the following two clinical cases seen in an oncology unit: Patient A: A 65-year-old smoker diagnosed with lung squamous cell carcinoma. Genomic analysis reveals…
Analyze the following two clinical cases seen in an oncology unit:
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Patient A: A 65-year-old smoker diagnosed with lung squamous cell carcinoma. Genomic analysis reveals inactivating mutations in the TP53 gene exclusively in cells from the tumor biopsy, but not in his blood lymphocytes or his sperm.
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Patient B: A 32-year-old woman diagnosed with bilateral breast cancer. Genetic testing detects a pathogenic mutation in the BRCA1 gene in all her somatic cells and in her oocytes, an alteration also present in her mother and maternal grandmother.
- a) Based on these data, refute the apparent contradiction in the statement "cancer is always a genetic disease, but rarely hereditary," by assigning and justifying for each patient the type of mutation (somatic or germline) and its impact on offspring.
- b) Applying Knudson's two-hit hypothesis for tumor suppressor genes, explain why Patient B developed the tumor at such an early age, and clarify why inheriting this germline mutation does not mean being born with an already developed tumor.
Cancer prevention
Name three lifestyle habits that reduce the risk of developing cancer and briefly explain why each has that protective effect.
Name three lifestyle habits that reduce the risk of developing cancer and briefly explain why each has that protective effect.
Back to the beginning: a mole that changes shape and color, grows and has ragged edges suggests a malignant tumor, probably caused by accumulated mutations from UV exposure. A dermatologist biopsies it, and sun protection lowers the risk.