OC 2- environmental aetiology Flashcards
What causes cancer?
all cancers result from mutations in genes
mutations in genes cause a cell to lose regulatory control so it grows at an uncontrolled rate, doesn’t repair damaged DNA and doesn’t undergo apoptosis
Can 1 mutation turn a cell cancerous?
no, it takes more than one mutation to turn a cell cancerous
How many genetic mutations have been shown to be associated with oral cancers?
up to 23
What genes are often targeted by mutations?
tumour suppressor genes like P53 and retinoblastoma gene
What can cause genetic errors?
can be inherited, can be caused by viruses, or develop as a result of exposure to chemicals or radiation
In head and neck cancer, what are genetic errors commonly caused by?
viruses
What areas can oral cancer affect?
the lips, salivary glands, tongue, gums, palate and inside of cheeks
What portion of the tongue is ‘oral/mouth’ and what portion is ‘oropharyngeal’?
Anterior 2/3 of tongue is oral/mouth tongue
Posterior 1/3 of the tongue is oropharyngeal tongue
What is the most common type of oral cancer?
Squamous cell carcinoma (90% of oral cancers)
What can ‘head and neck’ cancers affect?
throat (pharynx), voice box (larynx), salivary glands, nose, sinuses, lips and skin
Is oral cancer more common in males or females, and by what ratio?
more common in males, 2:1 M:F
What are the risk factors for oral cancer?
- tobacco
- alcohol
- poor diet/obesity
- sunlight
- immunological defect
- previous cancer
- genetic conditions
- potentially malignant conditions
- 25% of cases have no known risk factors
Smoking and alcohol consumption have a synergistic effect on oral cancer risk.
How much more at risk is a heavy smoker and drinker compared to a non smoker and moderate drinker?
24 times higher risk
What is the most common site for oral cancer? Why?
under the tongue/FOM - pooling of carcinogens in the saliva
Why does alcohol increase the risk of oral cancer?
Alcohol causes thinning/atrophy of the oral mucosa, making it more permeable to the carcinogens - entry of carcinogens into the epithelial cell barrier easier
How many harmful chemicals compounds does tobacco smoke contain?
more than 4000
What are the relative risks of someone who smokes <10 cig/day, <20 cig/day and >20 cig/day?
<10 cig/day - 2.5
<20 cig/day - 5.0
>20 cig/day - 5.5
What is the relative risk of a current smoker vs a former smoker?
current smoker - 3.4
former smoker - 1.4
Does quitting smoking ever reduce your relative risk?
after quitting, it takes 20 years for relative risk to be the same as that of a never smoker
What are some of the cancer causing chemicals involved in smoking?
tar, arsenic, polycyclic aromatic hydrocarbons (eg. benzopyrene), nitrosamines, acrolein (mutagen, carcinogen)
other poisons in tobacco smoke include:
- hydrogen cyanide, CO, ammonia
What is the relative risk for betel quid use?
2.4
What is the relative risk for betel quid + tobacco?
8.5
What is the pathogenesis for betel quid use?
- arecoline, an alkaloid in the nut, has been shown to stimulate collagen synthesis by 170%
- tannins present in the nut increase the resistance of collagen degradation
-> excessive collagen build up, scarring and restriction of mouth opening - alkaloid causes DNA damage
- lime can release reactive oxygen species from extracts of betel nut
What is alcohol metabolised to?
acetaldehyde
Where is alcohol metabolised?
salivary glands, mucosa, oral bacteria - hence exposure of these areas to acetaldehyde
What enzyme breaks down ethanol?
alcohol dehydrogenase
What enzyme breaks down acetaldehyde?
aldehyde dehydrogenase
What are the alcohol recommendations in the UK?
- 14 units/week
- at least 2 alcohol free days/week
- binge M >8 units, F >6 units
- pregnancy - no safe limit, don’t drink
Why was the alcohol limit lower for women?
- women’s bodies have higher proportion of body fat and less water than men = conc. of alcohol in body water is higher
- women have higher blood alcohol levels due to lower gastric ADH activity
On average how long does it take to eliminate 1 unit of alcohol from the body?
1 hour (think 1 unit = 1 hour)
What proportion of Scots binge drink?
1/3
What vitamins etc. sourced from food can be effective in prevention of oral cancer?
- vitamin C
- vitamin E
- antioxidants
- zinc
- beta-carotene
- folate
If someone is iron deficient, how can this increase their oral cancer risk?
If someone is iron deficient, they have low folate stores which can cause their mucosa to thin and increase the permeability - more readily accessible for carcinogens
Is obesity a risk factor for oral cancer?
studies have suggested that obesity is linked to the risk and survival for head and neck cancers
What factors are associated with lower lip cancer?
UV light, HPV, and immunosuppression
