Cervical Screening Flashcards
12% of human cancers are caused by viruses. Which viruses are implicated?
- HBV
- HIV
- EBV
- HPV
how common is HPV infection?
- very common
- lifetime risk of exposure 80% from serological studies
- peak prevalence 15-25 years, then declining with age
- 10% overall prevalence
- 30% prevalence in young women
HPV causes other less common cancers, list these
- cervix (> 99% cases caused by HPV)
- penis 40%
- vulva/vagina 40%
- anus 90% (hiher rates in men who have sex with men)
- mouth 3%
- oropharynx 12%
what is a squamous intraepithelial lesion (SIL)?
- an abnormal growth of squamous cells detectable on a smear.
- such changes may be low grade (LSIL) or high grade (HSIL), depending on how much of the cervical epithelium is affected, and how abnormal the cells appear.
what is a cervical intraepithelial neoplasia (CIN)?
Abnormal cells in the cervix detected by biopsy and histological examination.
Graded 1-3 according to the proportion of cervix affected.
which papilloma virus types are responsible for approx 70% of cervical cancers in Europe?
16 & 18
describe the UK HPV immunisation programme
- 12 year old (girls and boys) receive a two dose regimen of a quadrivalent vaccine against HPV 16/18/6/11
why did we change from cytology to HPV testing for cervical screening?
- HPV testing is more sensitive than cytology for high grade abnormalities
- As more HPV-immunised women enter the screened population, cervical disease will decrease and will be more difficult to detect by cytology. HPV will be more effective test for the future.
- If the HPV test is negative, the woman’s chance of developing cervical cancer in the next 5 years is very small, allowing a 5 year screening interval for all women regardless of age.
- if HPV test is positive, then cytology is performed.
what are the nuclear features of abnormal cervical cells identified by cytology?
abnormal = dyskaryosis
- can be low-grade or high-grade
Nuclear features:
- increased size and nuclear:cytoplasmic ratio
- variation in shape, size
- coarse irregular chromatin
- nucleoli
what happens next if a cytology identifies abnormal cervical cells (dyskaryosis)?
Refer to Colposcopy:
- magnification and light to see cervix
- exclude obvious malignancy
- use of acetic acid +/- iodene to identify limits of lesion, select biopsy site and define area to treat.
Colposcopy options for management
- punch biopsy to make diagnosis
- return for treatment if biopsy CIN 2/3
- ‘see and treat’ at first visit if obvious high-grade lesion
how does HPV target the transformation zone of the cervix?
squamo-columnar junction
- infects basal layer cells
- utilises host for replication
- as host cell matures, different viral genes are expressed, examples: E7 protein product - prevents cell cycle arrest, E6 protein product - inhibits cell death.
describe Koilocytosis
- a feature of HPV histology
- cells with wrinkled nucleus and perinuclear halo
- multinucleation
what are the low-risk types of human papilloma virus?
6, 11, 42, 44
- typically associated with genital warts and low-grade CIN
- often transient and resolve
what are the high-risk types of HPV?
- 16,18, 31, 45
- peristent infection increases risk of developing high grade CIN and (more rarely) cancer
how does HPV cause high grade CIN?
Persistent infection:
- viral DNA integrates into host cell genome
- overexpression of viral E6 and E7 proteins
- deregulation of host cell cycle
what is considered a CIN3?
- Neoplastic cells or undifferentiated cells fill full thickness of epith here , no normal differentiated cells seen = CIN3
what is considered a CIN2?
When undiffer cells occupy 2/3 of thickness and only top layers show maturation to medium size cells = CIN2
what is considered a CIN1?
If undiff cells only occupy lowest 1/3 of epith and surface cells can mature to big flat cells = CIN1
