Biochemical tumour markers in blood:

• Biochemical — measured by laboratory assays
• Elevated in patients with tumour
• Related to total tumour burden ^[1]

The key nuance the lecturer raises: "To what extent is this true?" — meaning tumour markers are imperfect. They can be elevated in benign conditions, they are not always proportional to tumour burden, and they have variable sensitivity and specificity. This is why most tumour markers are NOT suitable as stand-alone screening tests.

The slide also quotes the Wikipedia definition of a tumour marker: "A biomarker found in blood, urine, or body tissues that can be elevated by the presence of one or more types of cancer… An elevated level of a tumor marker can indicate cancer; however, there can also be other causes of the elevation (false positive values)." Tumour markers can be produced directly by the tumour or by non-tumour cells as a response to the presence of a tumour ^[1].

Are there non-biochemical markers? Yes — genetic markers:

• Cytogenetic markers (e.g., Philadelphia chromosome in CML)
• Plasma nucleic acid (e.g., circulating tumour DNA, ctDNA)
• Specific mutations (e.g., EGFR in lung cancer)
• Genomic changes (e.g., microsatellite instability)

What can we do with tumour markers?

1. Screening
2. Diagnosis
3. Determine modality of treatment
4. Monitoring disease progression
5. Detection of relapse
6. Prognostication

Why this ordering matters: Most tumour markers are better at monitoring/relapse detection than at screening. Screening requires very high sensitivity and specificity in a low-prevalence population — most tumour markers fail this bar.

• Suspected medullary thyroid carcinoma → Calcitonin, [Procalcitonin]
• Suspected hepatocellular carcinoma → Alpha-fetoprotein

Serial monitoring examples:

• CA-125 in ovarian cancer
• CEA in colon cancer / lung cancer
• Thyroglobulin in differentiated thyroid carcinoma

The principle is to compare serial results with the tumour type, pretreatment level, treatment and imaging. A falling marker may support response and a confirmed rising trend may prompt evaluation for progression or recurrence, but neither pattern is absolute: not every tumour secretes the marker, clearance takes time, benign conditions interfere, and recurrence still requires clinical/radiological correlation. ^[12]

The slide's historical burden estimates:

• Worldwide incidence: 1.6M per year
• Deaths: 366k per year
• American lifetime risk of disease: 16%
• Risk of dying from prostate cancer: 2.9% ^[1]

The absolute values depend on year and population, but the visual lesson is durable: diagnosis is much more common than death. Some screen-detected cancers are indolent, so shared decision-making must balance reduced metastatic disease/mortality against false positives, biopsy harms, overdiagnosis and treatment morbidity.

• Prostate-specific antigen = Human kallikrein 3
• Serine protease (an enzyme)
• Complexed with serum anti-proteases: α1-anti-chymotrypsin, α2-macroglobulin

PSA is prostate-specific but NOT prostate-cancer-specific ^[3]. It is also elevated in:

• Benign prostatic hyperplasia (BPH)
• Prostatitis
• Prostatic infarction
• Acute urinary retention
• Prostate manipulation (biopsy, TURP, DRE — though DRE causes only minimal transient elevation)
• Ejaculation (returns to normal within 48 hours)
• Cycling/perineal trauma

PSA Processing and Isoforms [1]

The slide shows the intracellular processing pathway of PSA:

1. PreproPSA (261 aa) → cotranslational cleavage → [−7]proPSA (244 aa)
2. [−7]proPSA → proteolysis by hK2, hK4 → mature active PSA (237 aa)
3. Mature PSA undergoes internal cleavage (residues 85–86, 145–146, 182–183) → BPSA and iPSA (inactive forms)
4. [−7]proPSA can also degrade into inactive truncated forms: [−5]proPSA, [−4]proPSA, [−2]proPSA, [−1]proPSA

In blood, the measurable forms include complexed PSA (cPSA, bound to protease inhibitors), BPSA, iPSA, and the truncated proPSA isoforms. [−2]proPSA (p2PSA) is the isoform used in the phi calculation ^[1].

The lecture's historical data set labels:

• < 4 ng/mL: “negative” (Sn = 78%, Sp = 33%)
• > 10 ng/mL: “positive” (Sn ~40%, Sp ~90%)
• 4–10 ng/mL: “troublesome” (the classic “grey zone”)
• AUC = 0.58 in the cited cohort ^[1]

Why is the 4–10 ng/mL zone problematic? Benign and malignant distributions overlap. The slide-era estimate of 20–25% biopsy positivity is not a personal post-test probability; prevalence, age, examination, prostate volume, MRI, prior biopsy and the biopsy endpoint (any cancer versus clinically significant grade-group ≥2 disease) all change risk.

phi = p2PSA / free PSA × √PSA

In the slide's cited validation cohort, phi discriminated biopsy-detected prostate cancer better than %p2PSA, %free PSA or PSA alone, but was fairly expensive. ^[1]

The displayed phi bands and probabilities are assay/cohort estimates, not universal biopsy instructions. Today, phi is one optional secondary risk-stratification test alongside other serum/urine biomarkers, validated calculators and mpMRI; use it only when the result would change management. ^[13]

It takes 10 years on average to develop from adenomatous polyp to invasive carcinoma

This long preclinical window (the adenoma-carcinoma sequence) is what makes colorectal cancer an ideal candidate for screening — there is ample time to detect and remove polyps before they become malignant.

Polyps:

• Adenomatous vs hyperplastic
• Small vs large

Conventional adenomas and sessile serrated lesions are important precursors. Most small distal hyperplastic polyps have little malignant potential, but “serrated” is not synonymous with benign. Size, number, histology, dysplasia and location determine risk.

Radiological: Barium enema; CT colonography Biochemical: Faecal occult blood (different types); Faecal DNA Endoscopic: Flexible sigmoidoscopy; Colonoscopy; capsule endoscopy Combinations ^[1]

This is the slide's survey, not a current menu of equal options. Double-contrast barium enema is now rarely used for screening, and colon capsule is not a routine stand-alone average-risk screening test. A positive stool or CT-colonography test requires colonoscopy; colonoscopy can diagnose and remove precursors in the same procedure. ^[14]

EGTM guideline — Recommended: CEA

• Prognosis
• Surveillance following resection
• Monitoring therapy in advanced disease Faecal occult blood tests: Screening > 50 years of age “DNA tests not recommended at present” — the 2007 EGTM slide position ^[1]

Stool-Based DNA Markers Under Investigation [1]

The EGTM guideline lists DNA markers being studied for CRC screening:

This table is historically useful for the adenoma–carcinoma sequence, but the recommendation is outdated internationally: multitarget stool DNA–FIT is now an accepted option in some jurisdictions, and other stool/blood molecular tests have regulatory approval. They are not part of the current Hong Kong government FIT pathway, and every positive non-colonoscopy test still needs colonoscopy. ^[14][15]

Key concept: CEA is NOT used for screening of colorectal cancer. It is used for prognosis, post-operative surveillance (serial measurements to detect recurrence), and monitoring response to treatment in advanced disease. This is a common exam trap.

Slides 36–37 are screenshots of the 2016–2017 pilot, including its initial birth-cohort roll-out and two-stage FIT→colonoscopy pathway. Do not use the old cohort numbers as current eligibility. The current government programme covers asymptomatic residents aged 50–75; higher-risk people need an individualised earlier/more frequent strategy. ^[15]

This section discusses dihydropyrimidine dehydrogenase (DPD/DPYD) deficiency in the context of 5-fluorouracil (5-FU) and capecitabine toxicity. The slide references the paper: Tong CC, Lam CW, et al. A Novel DPYD Variant Associated With Severe Toxicity of Fluoropyrimidines: Role of Pre-emptive DPYD Genotype Screening. Front Oncol. 2018 ^[1].

5-Fluorouracil (5-FU) is a fluoropyrimidine antimetabolite used in several solid tumours. Its active metabolites inhibit thymidylate synthase (FdUMP), incorporate into RNA (FUTP) and can incorporate into DNA (FdUTP).

Orally administrable 5-FU prodrugs include tegafur, UFT (tegafur + uracil), S-1 (tegafur + CDHP + OXO), and capecitabine ^[1]. The composite slide 38 contrasts their design: uracil/CDHP intentionally inhibit DPD to sustain tegafur-derived 5-FU, while OXO modifies gastrointestinal phosphorylation; capecitabine is sequentially converted by carboxylesterase → cytidine deaminase → thymidine phosphorylase. The central pathway then shows the fork between dominant DPD catabolism to dihydrofluorouracil/FBAL and the much smaller anabolic fraction producing cytotoxic nucleotides. Do not combine a DPD inhibitor or extrapolate dosing across products outside an approved regimen.

DPD (dihydropyrimidine dehydrogenase) is the first and rate-limiting enzyme in the catabolism (breakdown) of 5-FU. 80–85% of administered 5-FU is catabolised by DPD (only 1–3% undergoes anabolism to active cytotoxic metabolites) ^[1]. The gene encoding DPD is DPYD.

Reduced DPD activity lowers systemic fluoropyrimidine clearance and raises exposure, causing severe and potentially fatal toxicity. Genotype is one predictor: allele function and the combined DPYD activity score matter, targeted panels miss rare variants, and a “wild-type” panel does not eliminate toxicity risk.

• Severe mucositis
• Myelosuppression (neutropenia, thrombocytopenia)
• Diarrhoea
• Hand-foot syndrome
• Neurotoxicity
• Death (in severe cases)

The lecture slide 39 shows a pathway diagram: "Disorders of the metabolism of purines, pyrimidines and nucleotides." DPYD deficiency falls under pyrimidine catabolism disorders. Dihydropyrimidine dehydrogenase converts uracil and thymine to their dihydro forms as the first step of degradation. When this enzyme is deficient:

• Endogenous biallelic DPD deficiency has a broad phenotype, from asymptomatic biochemical abnormality to childhood neurological disease.
• Pharmacologically, even partial deficiency can cause catastrophic systemic fluoropyrimidine toxicity.

April 1906 — the first histopathological findings of Alzheimer's disease reported by Dr. Alois Alzheimer

• Presented "peculiar severe disease process of the cerebral cortex" in the 37th Meeting of South-West German Psychiatrists

1. Amyloid-beta (Aβ) — forms extracellular amyloid plaques

   • Derived from cleavage of Amyloid Precursor Protein (APP) by β-secretase and γ-secretase
   • The 42-residue species is more aggregation-prone than Aβ40 and is central to amyloid biomarkers; “pathogenicity” is not captured by concentration alone

2. Tau — forms intracellular neurofibrillary tangles (NFTs)

   • Tau is a microtubule-associated protein that stabilises neuronal cytoskeleton
   • Abnormal phosphorylation, misfolding and aggregation contribute to loss of normal microtubule function and paired-helical/straight filaments

Slide 45 shows six adult CNS tau isoforms produced by alternative splicing: zero, one or two N-terminal inserts (0N/1N/2N) and either three or four microtubule-binding repeats (3R/4R). The adjacent map places many phosphosites and antibody epitopes across the projection, proline-rich, microtubule-binding and C-terminal domains. Red-labelled sites are enriched in AD in the source figure, whereas green/blue labels overlap normal-brain phosphorylation; the diagram therefore argues against treating “phosphorylated tau” as one uniform analyte. Clinical assays must specify the epitope (for example p-tau181 or p-tau217). ^[1]

The lecture references the AD continuum concept:

This is the older staged model reproduced on slide 46. It usefully separates amyloid, injury and clinical impairment, but the exact sequence is not deterministic and individual biomarkers overlap. Biomarker abnormality can precede symptoms by years; that does not mean asymptomatic population testing is currently recommended.

The NIA-AA 2018 research framework (Jack et al., 2018) classifies AD biomarkers into three categories:

• (A) Amyloid: CSF Aβ1–42, amyloid PET
• (T) Tau: CSF p-tau181, tau PET
• (N) Neurodegeneration: CSF t-tau, NfL, FDG-PET, structural MRI

In that research framework, A and T define Alzheimer pathologic change/disease; (N) stages non-specific injury and is not required to be positive. It was a research framework rather than a population-screening directive. The 2024 Alzheimer’s Association criteria instead group accurate amyloid PET, CSF ratios and validated plasma assays such as p-tau217 as early “Core 1” biomarkers, while still recommending clinical biomarker testing for symptomatic, not cognitively unimpaired, people outside research. ^[19]

The lecture references studies (Kivisäkk et al., Sci Rep 2024; Dulewicz et al., Int J Mol Sci 2022) on AD biomarkers:

CSF biomarkers (established):

• CSF Aβ42 — decreased (because Aβ42 is sequestered into plaques in the brain, less enters CSF)
• CSF total tau (t-tau) — often increased; a non-specific injury marker
• CSF phosphorylated tau (p-tau) — increased; some soluble p-tau species change early with amyloid biology and are not a direct count of tangles
• CSF Aβ42/Aβ40 ratio — decreased (more specific than Aβ42 alone)

Blood-based biomarkers (emerging):

• Plasma p-tau181, p-tau217, p-tau231 — highly promising; correlate with amyloid and tau PET
• Plasma Aβ42/Aβ40 ratio — decreased in AD
• Plasma GFAP (glial fibrillary acidic protein) — marker of astrocyte activation
• Plasma NfL (neurofilament light chain) — marker of neuronal injury (non-specific)

Plasma pTau217 — Diagnostic Performance [1]

Slides 47–49 show one Kivisäkk et al. (Sci Rep 2024) assay study. In two batches, p-tau217 values separate the labelled AD and control groups with a displayed AUC of 0.98 (95% CI 0.96–1.00); p-tau181 shows more overlap and AUC 0.86 (0.78–0.93). The paired scatterplots show plasma p-tau217 correlating with CSF p-tau181/t-tau and inversely tracking the CSF Aβ42/40 ratio more cleanly than plasma p-tau181. The red dashed thresholds are study/assay cut-points, not universal diagnostic values, and a case-control AUC can overstate performance in a mixed memory-clinic population. ^[1]