9.3
Tumor Progression
Tumor progression is a phenomenon where the pre-formed tumor acquires successive mutations to become clinically more aggressive and malignant. In the…
Tumor progression is a phenomenon where the pre-formed tumor acquires successive morphological and molecular changes to become more aggressive and malignant in its character.
Cancer begins as a single genetic change in a healthy cell, and with time, the progenies of that cell continue to proliferate and pass on the mutation to all the daughter cells. The genome of these mutant cells becomes increasingly unstable, allowing more mutations to accumulate.
For instance, in the initial stages of Chronic Myelogenous Leukemia or CML, the mutant cells exhibit a chromosomal aberration called the Philadelphia chromosome, which is formed by a reciprocal translocation, where the parts of chromosomes 22 and 9 swap places.
This creates a fusion protein BCR-ABL1 that helps cells increase the cell division rates, escape terminal differentiation, and avoid apoptosis, resulting in the accumulation of abnormal cells.
As the tumor progresses, the tumor cells stimulate the formation of new blood vessels around them by a process called angiogenesis.
These new blood vessels supply the cancer cells with oxygen, nutrients, and growth factors for rapid growth and proliferation. They also help the cancer cells to disseminate and travel to distant parts of the body and metastasize.
The parallel progression model best explains the tumor progression. According to this model, the breast cancer cells from the primary tumor, which is as small as 1 - 4 mm, can start to disseminate to distant organs and seed new tumors.
For the next 6 - 12 years, these seeds develop into secondary tumors in a parallel manner, each acquiring unique mutations at much faster rates. Such random mutations increase the chance of acquiring resistance to cancer treatment, jeopardizing the patients’ life.
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Q1: What is tumor progression and how does it develop?
Tumor progression is a phenomenon where a pre-formed tumor acquires successive morphological and molecular changes to become more aggressive and malignant. It begins when cancers originate from somatic mutations in a single cell, and over time, the mutant cell's progeny continue to proliferate and pass mutations to daughter cells. As the genome becomes increasingly unstable, more mutations accumulate, driving the tumor toward greater malignancy.
Q2: How does the Philadelphia chromosome contribute to chronic myelogenous leukemia progression?
In chronic myelogenous leukemia, the Philadelphia chromosome forms through a reciprocal translocation where parts of chromosomes 22 and 9 swap places. This creates a fusion protein called BCR-ABL1 that increases cell division rates, allows cells to escape terminal differentiation, and prevents apoptosis. These effects cause abnormal cells to accumulate, driving tumor progression.
Q3: What role does angiogenesis play in tumor progression?
As tumors progress, cancer cells stimulate the formation of new blood vessels through angiogenesis. These vessels supply oxygen, nutrients, and growth factors that enable rapid cancer cell growth and proliferation. Additionally, the new blood vessels facilitate cancer cell dissemination to distant body parts, enabling metastasis and secondary tumor formation.
Q4: How does the parallel progression model explain tumor dissemination?
The parallel progression model shows that breast cancer cells from a primary tumor as small as 1-4 millimeters can disseminate to distant organs and seed new tumors. Over 6-12 years, these seeds develop into secondary tumors in parallel, each acquiring unique mutations at faster rates. This random mutation accumulation increases resistance to cancer treatment, threatening patient survival.
Q5: What genetic changes occur during colon cancer progression?
Colon cancer progression involves sequential mutations in specific genes. Early mutations in the APC gene cause a small growth called a polyp. Further mutations in K-ras and p53 genes transform the benign polyp into a malignant tumor. At advanced stages, mutations in DCC and related genes contribute to tissue invasion and metastasis.
Q6: How do cancer cells escape normal cell cycle regulation?
Cancer cells overcome normal cell cycle regulation by skipping the resting G0 phase and progressing directly from the M phase to the G1 phase, allowing continuous division without terminal differentiation or apoptosis. They also overcome contact inhibition, a property that normally stops cell division when cells contact each other. This enables cancer cells to pile up and form tumor masses.
Q7: What three gene groups are critical for cancer progression?
Three important gene groups drive cancer progression. The first includes genes involved in cell growth and survival. The second comprises genes maintaining genetic stability, such as DNA repair enzymes. The third group involves genes controlling tissue invasion and metastasis, including those encoding cell adhesion proteins, proteolytic enzymes, and angiogenesis factors.