unit 9 - cancer Flashcards
neoplasia
“new growth” or tumor, a mass of tissue from abnormal proliferation of cells. can be benign or malignant (term cancer only applies to malignant tumors)
benign tumor characteristics
- resemble cell of origin (no anaplasia)
- cells tend to grow slowly
- well defined borders, remain confined to original location without invading surrounding normal tissue or spreading to other parts of the body
- no potential to kill host, but can still be life-threatening if in a dangerous location, such as the brain
- can be removed surgically
- warts are a type of benign tumor
malignant tumor characteristics
- high degree of anaplasia: cells lose resemblance to cell of origin and don’t divide and differentiate normally
- divide quickly and uncontrollably
- can metastasize AKA escape and invade other tissues, spreading through the lymphatic/circulatory systems
- greater degree of anaplasia = more aggressive cancer
carcinomas
tumor classification
* 90% of human cancers
* malignancies of epithelial cells, which divide more often so it’s easier for them to lose control
sarcomas
tumor classification
* 2% of cancers
* tumors of connective tissues (muscles, bones, or cartilage)
leukemias/lymphomas
tumor classification
* 8% of human cancers
* arise from blood-forming cells and immune system cells
properties/adaptations of cancer cells
- don’t display density-dependent/contact inhibition, where they stop proliferating and enter G0 phase
- don’t require growth factors or produce their own autocrine growth stimulations
- less adhesive than normal cells in cell-cell and cell-matrix interactions, which makes the cells rounder and allows them to metastasize
- secrete proteases that digest extracellular matrix components, which also helps them metastasize
- angiogenesis: cancer cells secrete growth factors that promote the formation of new blood vessels, which supplies it with oxygen and nutrients to continue growing
- anaplasia
- fail to undergo apoptosis
- produce the enzyme telomerase to protect their telomeres, so they can divide indefinitely without the limits of telomere degradation
- can “hide” from natural immune defenses by having sialic acid on the cell exterior or secreting chemicals that “confuse” T cytotoxic lymphocytes
steps in carcinogenesis
- initiation: DNA is damaged through mutation, can compound over time until it causes cancer
- promotion: proliferation of cells and growth promoters, activation of oncogenes
- progression: development of cancerous phenotype
carcinogenesis - initiation
- occurs when cell is exposed to mutagens/carcinogens– environmental factors, toxic chemicals, viruses, radiation
- if the damage to DNA occurs in genes that control cell division and differentiation, initiation occurs. usually due to accumulated mutations in several genes over time
- mutations lead to abnormal proliferation of a single cell
carcinogenesis - promotion
exposure of the mutated cell to factors that induce them to grow and proliferate exponentially, can happen directly after initiation or take years
promoting factors:
* hormones like estrogen
* dietary fat and high caloric intake
* food additives
* nicotine
* alcohol
* prolonged stress
carcinogenesis - progression
cells acquire properties that allow malignant behavior, increased growth rate
* develop telomerase enzyme
* tumors produce their own growth factors
* lack of contact inhibition
* induce angiogenesis
types of carcinogens
- oxygen radicals/reactive oxygen species - unpaired/extra electrons that are a byproduct of cellular respiration, can break the DNA backbone
- UV light exposure - UV-B that is mostly absorbed by the ozone layer but may penetrate, UV-C that is completely absorbed by the ozone layer. causes thymine dimers in DNA and causes skin cancer
- ionizing radiation - can break the DNA backbone
- chemical exposure - hydrocarbons found in smoke, gas, soot, tar, or aflatoxins produced in moldy corn/peanuts that create DNA mutations
- certain viral infections - introduce new genetic material into cells, cause 15% of all human cancers (examples: papillomavirus causes cevical cancer, Hep C causes liver cancer)
- replication errors
proto-oncogenes
- important cell regulatory genes that encode for proteins that function in the cell cycle and control of cell proliferation
oncogenes
proto-oncogenes that are mutated by carcinogens, are over-expressed and induce abnormal cell proliferation
what mutations have to happen to create a cancerous cell?
one dominant mutation (gain of function) in tumor development (oncogenes) OR two recessive mutations (loss of function) that cause inactivation of both copies of tumor suppressor genes
tumor suppressor genes
- inhibit cell proliferation by slowing down cell division, inducing DNA repair, or inducing apoptosis
- BOTH copies must be mutated for cancer to develop
- can inherit 1 defective copy from a parent–still need the other to mutate to develop cancer, but have a predisposition to it
Rb gene
type of tumor suppressor gene, produces the Retinoblastoma protein
* prevents passage from G1 phase of the cell cycle to S phase
* prevents replication when DNA is damaged by preventing chromatin condensation
BRCA1 and BRCA2 genes
tumor suppressor genes that lead to breast cancer if mutated
* involved in checkpont control of cell cycle progression and activate DNA repair of double strand breaks
* hereditary mutations can be inherited that increase the risk of developing breast or ovarian cancer
APC gene
tumor suppressor gene
adenomatous polyposis coli
* APC proteins are involved in cell adhesion, mutations lead to colon cancer and polyps/malignant ‘warts’ within the colon
* needs many more mutations to develop colon cancer (11)
steps of metastasis
- invasive tumor
grading and staging of tumors
grading: level of anaplasia, how much less differentiated are the cancer cells than normal cells. measures the potential aggressiveness of the cells to get an idea of how it may progress. done by looking at the cells under a microscope. 4 grades, with 4 being the worst/least differentiated
based on tubule formation, size/shape of cells, mitotic division
staging: how much the cancer has metastasized. stages from I-IV using TNM staging system
T: tumor size
N: spread to lymph nodes?
M: level of metastasis/how much it has spread, invading tissues?
diagnostic procedures for cancer detection
- x-rays
- PET scans - use a radioactive tracer to see progression of cancer treatments
- ultrasounds - use high-frequency sound waves to create an image of soft tissues
- MRI - uses magnetic fields and radio waves to create an image inside the body
- CT scans - fast series of x-ray pictures to create images of a scanned area
- endoscopy - provides direct view of a body cavity
- biopsy - removal of a portion of suspicious tissue, cells are then tested. only definitive method to diagnose cancer
- blood tests - test for presence of substances that aren’t found in the blood/urine except when cancer is present
cancer treatment methods
- Surgery
- Radiation Therapy
- Drug Therapy- Chemotherapy
- Immunotherapy
- Gene and Molecular Therapy
- Stem Cell Transplantation
steps of metastasis
- primary malignant tumor (invading nearby healthy tissue cells)
- angiogenesis: new vessel formation to feed the tumor
- cancer cells invade the lymph nodes and bloodstream, travels through it to another part of the body
- arrest in a distant capillary bed, start proliferating in a new area
