The nature of cancer Flashcards
a) define cancer
b) how genes can change
c) what fails in cancer
a) a disease caused by alteration of a cell’s genes. A normal cell successively acquires gene changes and becomes more and more abnormal as a result. Eventually it can become a cancer cell
b) i) mutations - in the most general sense, and kind of alteration of DNA sequence ii) epigenetic change - such as aberrant DNA methylation or histone modification iii) tumour viruses bringing extra genes into the cell. We don’t know how many gene changes are critical for cancer formation, but certainly 10 or more
c) Failure of 3D growth control and tissue repair, a failure of the mechanisms controlling development of complex structures, and repair of these if they are damaged, especially the spread of cells to inappropriate locations and growth here
Define
a) metastasis
b) malignant
c) benign
d) examples of cancers and where they metastasise to
a) formation of new colonies of tumour in other parts of the body, by the seeding of cells into the circulation. Such a colony is a metastasis and the process is also metastasis. The original tumour is the primary tumour, and a metastasis is the secondary
b) malignant tumours are those capable of metastasis. Tumour doesn’t have to have formed a metastasis to be malignant (the formation of metastasis is slow and may not have occurred)
c) benign tumours are those incapable of metastasis (unless subsequent mutation may turn the benign tumour into a malignant one
d) (see image). Cells from the malignant tumour get into blood or lymphatics and seed in other organs. Breast cancers often metastasise to the lungs and bone marrow, colorectal tumours often go to the liver
How to distinguish malignant tumours from benign histologically
Benign: Confined to their original site in the body. Have clearly defined boundaries and can be physically separated from surrounding tissue. Often surrounded by a capsule of connective tissue, which can be peeled away
Malignant: Ragged edges, infiltrating (invading) into surrounding tissue and growing there. Often show morphological differences such as abnormalities of nucelar size and shape, and alterations or loss of differentiation. Invasiveness is the most important quality
a) cancer developing in multiple stages (+ example in colorectal tumours)
b) relationship of malignant and benign tumours
c) danger of benign tumours
a) It takes many stages, corresponding to many gene changes, to produce a malignant tumour. The stages in the development of a cancer can often be recognised as abnormal tissue patterns
In colorectal cancer, a polyp (aka adenoma) precedes the malignant tumour.
b) malignant tumours often develop via visible benign precursors, but not all benign tumours give rise to malignant ones. eg the benign smooth muscle tumour of the uterus (leilyoma) doesn’t turn malignant (or very rarely)
c) benign tumours can kill, eg meningiomas in the brain or hormone-producing tumors of the pituitary/adrenal gland
Broad rule of naming tumours (+ examples)
Benign tumours - [name of tissue] + ‘oma’. eg lipoma (benign fat tumour), leiomyoma (benign smooth muscle tumour), papilloma (wart), adenoma (benign glandular polyp)
Malignant tumours from mesenchyme - [name of tissue] + ‘sarcoma’. eg osteosarcoma (malignant bone tumour), leiomyosarcoma (malifnant smooth muscle tumour)
Malignant tumours from epithelium - [name of tissue] + ‘carcinoma’. eg breast carcinoma (malignant breast tumour), colorectal carcinoma (malignant colorectal tumour)
Exceptions to the above rules - eg malignant melanoma (not used for benign moles), malignant neuroblastoma/glioblastoma of neural tumours
Haematopoietic system - leukaemias are liquid haematopoietic neoplasms, lymphoma are solid haematopoietic (usually lymphocytic) neoplasms
a) examples of how cancer interferes with normal function
b) metabolic effects of cancer
c) examples of how cancer causes death
a) i) pressure - enarged prostale obstructing ureter, meningioma on brain ii) erosion/destruction - eg of bone leading to fractures iii) epithelial ulceration - bleeding from colorectal tumours leading to anaemia iv) competition with normal function - failure of normal bone marrow in leukaemia
b) General - systemic wasting (cachexia). Specific (tumour-specific products) - eg peptide hormones ACTH, ADH secreted by small cell lung cancer. Cachexia refers to the general wasting often seen in cancer, the mechanism is unknown
c) Cause of death is generally more of a) and b), reflecting massive tumour burden. eg liver overwhelmed by metastatic colon cancer leading to liver failure, failure of normal bone marrow in leukaemia leads to infection through lack of neutrophils or haemorrhage due to lack of platelets, pain management by analgesia leads to respiratory depression
Screening for cancer
a) objective
b) cervical cancer
c) colorectal cancer
d) breast cancer
a) find cancer earlier, ideally before tumour becomes malignant. The ideal screen would be to find benign precursors of cancer and remove them before they turn malignant
b) Benign precursor lesions can be detected by a cervical smear test, where the cells from the cervix are sampled by scraping and collecting. Decreased incidence of cervical cancer in countries that screen for it strongly suggests this is a useful strategy.
c) Screening currently done by detecting blood in stoll collected at home, although this is only able to detect tumours that have already ulcerated. Endoscopy for polys would be better, detecting the precursor, but this is much more expensive and demanding on the patient
d) Decected by X-ray mammography, slightly earlier than it would be detected by palpation. This is expensive and demanding for patients, and the value of screening is highly controversial
