15.1 What impact has the introduction of liquid based cytology had on automated screening?
Liquid based cytology preparations produce a ‘near monolayer’ compared to conventional slides, which could be multiple layers thick. LBC preparations are easier to scan and digitally capture images for review.
15.2 What are the potential benefits of automated screening?
- Improved sensitivities, specificity, and accuracy compared to manual screening. This is influenced by the quality of manual screening in different countries and whether devices are used for primary screening or quality control.
- Reduced false negatives.
- Reduced false positives and risk of over-treatment especially in women of childbearing age.
- Automation applies a standardized measurements rule, which eliminates human bias and subjectivity.
- Increased productivity.
- Triaging (sorting) slides for review and using an interactive approach brings greater job satisfaction to the cytologist by concentrating their skills set on slides requiring more expert interpretation.
15.3 Why is HPV testing a less than ideal primary screening tool in the under 35-year-olds?
HPV testing is a highly sensitive test but is less specific in younger women (<35). Most women will test positive for transient HPV which will clear the system given time. Persistent HPV is the cause of cervical abnormalities and cancer. HPV testing will play a key role in managing low-grade abnormalities and as a test of cure. Whether it can replace cytology as a primary screening tool in under 35-yearolds is still being debated across professional groups.
15.4 What impact will the vaccine have on the cervical screening programme?
As the uptake of the vaccine increases the true success will become more evidence based. This is expected to lead to a decrease in the disease and in turn a decrease in the number of cervical tests. In the short, medium, and long term cytology will continue to play a key role, as for a generation there will be two populations to screen: a vaccinated and an unvaccinated population.
15.5 Why is determining HER2 status important in patients with breast cancer?
Patients who are identified as HER2 positive by immunohistochemistry or FISH can be treated with Herceptin, which has been proved to act against the cancer and prolong survival.
15.6 What are the advantages of FISH over immunocytochemistry?
FISH analysis is more sensitive and can detect chromosomal changes as well as producing a signal which can be quantifi ed. It is of most benefi t when cytomorphological changes are equivocal, e.g. in HER2 breast scoring 2 and follow-up of patients with a previous bladder cancer.
15.7 What are the limitations of FISH analysis?
FISH is not available in routine settings, requires a specialist setting, expensive, little gain in turnaround times, diffi cult to detect very small changes.
15.8 What is meant by a tumour of unknown origin?
To treat cancer it is important to establish the primary (site of origin) to guide the clinical team to the best form of therapy for the cancer. The patient has a poor prognosis if the primary site cannot be confirmed. Molecular techniques using tissue microarrays are expected to improve the science by carrying out multiple parallel testing on samples to help diagnose site of origin.
15.9 What are the advantages of tissue microarray analysis?
Tissue microarray analysis allows standardization of preparations and is economical with tissue, whilst preserving the original block. It has potential to be cost effective as multiple tests can be performed on a single microarray as opposed to multiple tests on multiple samples. Different molecular techniques can be applied to the array to complement the morphological diagnosis.
15.10 Explain the difference between signal and target amplification.
Target amplification occurs when single-stranded target DNA is amplified using a probe. This will result in multiple DNA copies by increasing the number of nucleic acids being produced. Polymerase chain reaction is an example of target amplification. Signal amplification, on the other hand, amplifies the signal in the presence of DNA without an increase in the amount of nucleic acids. HC2 is an example of signal amplification.
15.11 Why has PCR revolutionized molecular testing?
Polymerase chain reaction is a method for producing large amounts of a specific DNA fragment of a defined sequence from a small amount of DNA. It can amplify a single molecule of DNA or RNA several million-fold in a few hours. PCR enables the detection and analysis of specific gene sequences in a patient’s sample. Analyses can be performed on a few cells from body fluids or in a drop of blood. Thus, PCR eliminates the need to prepare large amounts of DNA from tissue samples.
15.12 Explain the benefits of laser microdissection.
Laser microdissection is a technique which can be used to extract cells of interest (usually tumour) from very sparse samples in paraf- fi n blocks or direct from cytological preparations, avoiding necrotic and fi brotic debris. Cells can then be sent for mutational analysis. One example would be cells obtained from a non-small cell carcinoma during an EBUS procedure and sent for EGFR testing.
15.13 In what scenario may it be useful to carry out FISH analysis on patients with a previous bladder cancer?
Patients who have had treatment for bladder cancer have to have regular follow-up cystoscopies and cytology. The cytology can show changes which may be difficult to diagnose. In this instance it can be of diagnostic benefit to send a cytology sample for FISH analysis to either confirm or rule out a recurrent tumour.
15.14 Why is EGFR positivity important in patients with non-small cell carcinoma?
Some non-small cell lung cancers over express EGFR positivity and increased tyrosine kinase activity. NICE has recently approved the use of IRESSA (gefi tinib) a TK inhibitor drug which can slow tumour growth and improve patient survival. Only patients with EGFR positive tumours are given the drug.
15.5 What is the significance of the telomerase gene TERC in cancer?
Telomerase is an enzyme which is responsible for adding DNA sequences to DNA strand within the telomere region of the chromosome. Activation is common in cancers; drugs are being developed to switch off telomerase activity.