W29 L3 - Molecular biomarkers of cancer

MG

what are biomarkers

measurable indicators in the body that signal the normal biological processes, disease presence/risk, or how a body responds to treatment, acting as objective clues for doctors to diagnose monitor, and personalise medicine

• a naturally occurring molecule, gene, or characteristic by which a particular pathological or physiological process, disease, etc. can be identified

• can be as simple as blood pressure or complex DNA/protein changes in blood or urine providing vital insights into health status

what is a molecular biomarker

a biological molecule found in blood, other body fluids, or tissues that is a measurable indicator in the body 

that signal the normal biological processes, disease presence/risk, or how a body responds to treatment, acting as objective clues for doctors to diagnose monitor, and personalise medicine

what can molecular biomarkers be used for

• prevention - help prevent cancer by understanding the risk of developing it

• detection - screening for cancer

• diagnosis - identification of cancer type

• prognosis - predicted outcome (±treatment)

• treatment - guiding decisions

• treatment response - monitor/predict treatment response

• cancer recurrence

sometimes biomarkers are used for more than one thing

• e.g for both cancer diagnosis and treatment

which phrases in cancer research treatment are often used interchangeably

molecular biomarker of cancer

• cancer biomarker (UK)

• tumour biomarker (US)

what is investigating the presence/absence or level of a cancer biomarker part of

molecular pathology

• the study of molecules in a disease state

• generally involves isolation, detection and analysis of DNA, RNA, protein

what are some technologies for the detection of cancer biomarkers

• radioimmunoassay (RIA)

• immunohistochemistry

• PCR

• fluorescent immunoassay

what is radioimmunoassay

a highly sensitive in vitro laboratory technique used to measure the concentration of antigens (e.g., hormones, drugs) in biological samples.

• Developed in the 1950s by Yalow and Berson

• it uses radioactive isotopes (often I-125) to label antigens, which then compete with unlabeled antigens in a patient sample for a limited number of antibody binding sites (competitive binding)

• the more unlabeled antigen present in the sample, the less labeled antigen binds to the antibody, resulting in lower radioactivity in the complex.

what is immunohistochemistry

a method to detect the distribution of antigens (or antibodies) on formalin-fixed paraffin-embedded (FFPE) tissue sections which is then seen under a microscope

what is PCR

a molecular biological technique used to amplify specific DNA fragments

what is fluorescent immunoassay (FIA)

a highly sensitive, rapid diagnostic technique that uses fluorescent-labeled antibodies to detect and quantify antigens, hormones, or drugs in samples

• intensity of the emitted light from the fluorescent tag on the antibody is measured. The brighter the "glow," the more of the target molecule is present in the sample.

what should the ideal biomarker be

100% sensitive. - always correctly positive

100% specific - always correctly negative

what is sensitivity

the percentage of test results which are correctly positive

• greater the sensitivity, the fewer the false-negatives

what is specificity

the percentage of test results that are correctly negative

• greater the specificity, the fewer the false-positives

what is the equation for sensitivity

true positive rate (TPR) = TP / (TP+FN)

true pos

fals neg

what is the equation for specificity

true negative rate TNR = TN/(TN+FP)

true neg

false pos

what is the focus of sensitivity vs specificity

sensitivity - detecting disease presence

specificity - ruling out disease absence

what is minimised in sensitivity vs specificity

sensitivity - false negatives

specificity - false positives

what is a typical use case in sensitivity vs specificity

sensitivity - screening tests where missing disease is risky

specificity - confirmatory tests where false alarms are problematic

what is PSA

prostate specific antigen

• a protein that is made by prostate cells (it is a cancer biomarker)

what is a prostate

a walnut sized gland that surrounds the urethra below the bladder

• produces seminal fluid to support sperm viability and carries the sperm

how is PSA measures

using a fluorescent immunoassay using a blood sample

when can PSA levels be raised

number of conditions

• urinary infection

• an enlarged prostate

• prostatitis

• prostate cancer

why does the UK National Screening committee not recommend whole population screening for prostate cancer using the PSA test

• Low Test Accuracy: The PSA test is not accurate enough to distinguish between aggressive cancers and slow-growing ones that would never cause harm, resulting in many false positives and false negatives.

• Overdiagnosis and Overtreatment: Screening identifies many indolent cancers, leading to unnecessary biopsies and treatments (surgery or radiotherapy) that can cause long-term side effects like incontinence and impotence when the cancer wouldn’t have affected length of life or caused symptoms

  • biopsies also carry a risk of rectal bleeding, blood in urine, blood in semen, infection, urinary difficulty, pain and worry. 

  • causes unnecessary worry to men and other psychological harms such as anxiety, fear of cancer, and undue stress lasting long periods of time

• Unclear Benefit: The evidence does not clearly show that population-wide screening significantly reduces mortality from prostate cancer.

what is the TRANSFORM trial

a £42 million trial for prostate cancer screening

• designed to find the best way to screen men for prostate cancer,

• testing the most promising screening techniques available, including PSA blood tests, genetic tests (polygenic risk scores) and fast MRI scans, combined in ways that have never before been tested in a large-scale screening trial

• 2025 start

• at least 1/10 invited will be black men

How can prevention be undertaken

can undergo tests that look for inherited genetic disease, assess cancer risk and allow for preventative measures to be given to the tested patients and/or their relatives

• mutations APC (colon cancer)

• mutations in BRCA1 and BRCA2 genes (breast and/or ovarian cancers)

what is the process for testing for mutations in BRCA1 and 2 genes

• genetic counselling

• blood or saliva (home) test

• BRCA1 and 2 genes are checked for mutations - PCR analysis for specific mutations or whole gene DNA sequencing

• result and genetic counselling

• BRCA1 and 2 genes are cancer biomarkers

What did Angelina Jolie do and why

• underwent a preventive double mastectomy after testing positive for the inherited BRCA1 gene mutation.

  • This mutation gave her an estimated 87% risk of breast cancer and a 50% risk of ovarian cancer

• she also removed her ovaries and fallopian tubes, her mother had ovarian cancer

• Her disclosure led to a significant, though temporary, increase in genetic testing for BRCA mutations

what % of all breast cancers are due to inheriting a faulty gene

3-5% familial breast cancer

• inherited mutations in either BRCA1 or BRCA2 genes increase risk

what is the lifetime risk of developing breast cancer if you have a mutated BRCA1 or BRCA2 gene

up to a 90% lifetime risk of developing breast cancer

what is the lifetime risk of developing ovarian cancer if you have a mutated BRCA1 or BRCA2 gene

55% increase risk with BRCA1

25% increase with BRCA2

what are people with a mutated BRCA1 or BRCA2 gene likely to acquire

• a second mutation (loss of heterozygosity/LOH) leading to dominant expression of the cancer

what type of genes are both BRCA1 and BRCA2

tumour suppressor genes

• proteins from these genes are involved in DNA repair

what is the FIT (cancer detection)

faecal immunity test

• a type of faecal occult blood test

• used for National Bowel (colorectal) Screening Programme

how does FIT work

• uses antibodies that specifically recognise human haemoglobin (Hb) protein - cancer biomarker

• an immunoassay used to detect and quantify the amount of human blood in a single stool sample

• abnormal result suggests there may be bleeding within GI tract that needs to be investigated

  • those with abnormal results are invited for further testing via a diagnostic procedure

What is HPV

Human Papilloma Virus

• 77 known types

• sexually transmitted

• most types don’t cause symptoms

• some types may cause genital warts (HPV6, HPV11)

what are the high risk types of HPV and what can this cause

• HPV16 and HPV18

• may persist and eventually cause cancer (cancer biomarkers)

• high risk HPV types cause 99.7% of cervical cancers

what can a HPV infection increase the risk of, how is this detected

• high cervical cancer risk

• get screened for HPV infection - check for presence of HPV DNA

how is the test for HPV undergone

• cells are brushed from the cervix using a surgical broom

  • head of brush device is rinsed or broken off into a vial of preservative fluid so that most of the cells are retained in vial

• cells are checked for presence of high risk HPV via detection of viral DNA by PCR

  • HPV16 and 18

• if HPV positive then same sample checked for abnormal cells (cytology)

• if positive for abnormal cells then follow up with detailed examination of the cervix by colposcopy

what are common cancer biomarkers used to diagnose cancer

• Carbohydrate antigen 125 (CA125)

• Carbohydrate antigen 19-9 (CA19-9)

what is CA125

• large glycoprotein ~22,000 amino acids

• encoded by the MUC16 gene

• membrane associated with a single transmembrane domain

give examples of biomarkers looked at for prevention, detection, and diagnosis

prevention - BRCA1 and BRCA2

detection - FIT and HPV test

diagnosis - CA125 and CA19-9

where is CA125 found

found on the apical surfaces of corneal/conjunctival, respiratory, and female reproductive tract epithelia

what is raised in 90% of patients with advanced ovarian cancer

CA125

how do you test for CA125

fluorescent immunoassay on blood sample

• used in combination with other tests to diagnose cancer

when else can CA125 be raised

in non-cancerous conditions

• endometriosis

• acute pancreatitis

• cirrhosis

• peritonitis

• inflammatory pelvic disease

what is CA19-9

• a cell surface glycoprotein complex

• mostly associated with pancreatic ductal adenocarcinoma (PDAC)

• released by PDAC cells

how do you test for C19-9

radioimmunoassay on a blood sample

• considered the most useful blood test for signalling the presence of PDAC versus benign pancreatic disorders

• also used to monitor response to treatment

• used in combination with other tests to diagnose cancer