Questions
Merkel cell polyomavirus: Questions
Study questions about Merkel cell polyomavirus: multiple-choice, clinical scenarios, short-answer and exam-style.
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6 questions: 5 MCQ, 1 written.
High prioritySAQWrite short notes on Merkel cell polyomavirus. [5]
Model answer
- Classification: a small non-enveloped double-stranded DNA virus of the family Polyomaviridae, genus Alphapolyomavirus, with a circular genome of about 5 kilobases.
- Skin commensal: a near-universal component of the normal skin flora, acquired in childhood and carried lifelong without symptoms, with adult seroprevalence around 60 to 80%.
- Causal role in cancer: the established cause of about 80% of Merkel cell carcinomas, making it the only human polyomavirus with a proven oncogenic role; the remaining Merkel cell carcinomas are ultraviolet-driven and virus-negative.
- Oncogenic mechanism: in the tumour the viral genome is clonally integrated into host DNA and expresses a truncated large T antigen that retains the retinoblastoma protein (RB)-binding region but has lost the capacity to replicate the virus, so it drives proliferation, while the small t antigen supports transformation.
- Merkel cell carcinoma: an aggressive cutaneous neuroendocrine carcinoma presenting as a rapidly enlarging, painless red or violet nodule on sun-exposed skin of older or immunosuppressed people, identified histologically by a dot-like cytokeratin 20 pattern and treated in advanced disease with programmed death-1 (PD-1) or its ligand (PD-L1) checkpoint inhibitors.
- MCQ
A typical Merkel cell carcinoma presents as:
- A. A slowly growing pigmented mole with irregular borders and colour variation
- B. A chronic non-healing ulcer on the lower leg
- C. A rapidly enlarging painless red-violet nodule on sun-exposed skin
- D. A scaly premalignant patch on the balding scalp
- E. A pearly papule with a rolled telangiectatic edge
Show answer
Correct answer: C
Merkel cell carcinoma classically appears as a firm, painless, rapidly enlarging red or violet nodule on sun-exposed skin of an older person, summarised by the AEIOU features (asymptomatic, expanding rapidly, immunosuppressed, older than 50 years, ultraviolet-exposed skin).
A pigmented irregular mole suggests melanoma, a pearly telangiectatic papule basal cell carcinoma, and a scaly patch actinic keratosis or squamous carcinoma.
- MCQ
Merkel cell polyomavirus is best characterised as:
- A. An enveloped RNA virus that spreads between people through the respiratory route
- B. The only human polyomavirus proven to cause a human cancer
- C. A herpesvirus that establishes lifelong latency in sensory neurons
- D. A retrovirus that integrates at random genomic sites
- E. A papillomavirus that causes cutaneous warts
Show answer
Correct answer: B
Merkel cell polyomavirus is a non-enveloped double-stranded DNA polyomavirus (genus Alphapolyomavirus) and the only human polyomavirus with a proven causal role in a human cancer, Merkel cell carcinoma.
It is not an RNA virus, a herpesvirus, a retrovirus or a papillomavirus.
- MCQ
The standard treatment for metastatic Merkel cell carcinoma is:
- A. High-dose intravenous aciclovir
- B. Cidofovir given with probenecid cover
- C. Combination cytotoxic chemotherapy as the long-term mainstay of care
- D. Reduction of immunosuppression as the sole measure
- E. Immune checkpoint inhibitors targeting PD-1 or PD-L1
Show answer
Correct answer: E
Because the tumour expresses foreign viral antigens and is immunogenic, immune checkpoint inhibitors directed at programmed death-1 (PD-1) or its ligand (PD-L1) are now the standard treatment for metastatic Merkel cell carcinoma, having displaced cytotoxic chemotherapy.
Aciclovir and cidofovir have no role, and reducing immunosuppression assists but is not sufficient alone.
- MCQ
Which best describes the natural history of Merkel cell polyomavirus?
- A. Lifelong asymptomatic skin carriage, cancer a rare late event
- B. Acute hepatitis followed by a lifelong risk of cirrhosis and liver cancer
- C. Latency in sensory ganglia with painful cutaneous reactivation
- D. Persistent renal infection causing transplant nephropathy
- E. Chronic productive infection of the respiratory epithelium
Show answer
Correct answer: A
The virus is a near-universal skin commensal acquired in childhood and carried for life without symptoms; Merkel cell carcinoma is a rare late event in older or immunosuppressed people.
The other options describe hepatitis viruses, herpesviruses, BK virus and respiratory viruses respectively.
- MCQ
Which biopsy finding best supports a diagnosis of Merkel cell carcinoma?
- A. Koilocytes with perinuclear haloes
- B. Owl-eye intranuclear inclusion bodies
- C. Multinucleated giant cells with Cowdry type A inclusions
- D. Small blue cells with dot-like cytokeratin 20 staining
- E. Acantholytic cells overlying a tense subepidermal blister
Show answer
Correct answer: D
Merkel cell carcinoma is a small round blue cell tumour with neuroendocrine differentiation, identified by a characteristic paranuclear dot-like cytokeratin 20 pattern with synaptophysin and chromogranin.
Koilocytes indicate human papillomavirus (HPV), owl-eye cells cytomegalovirus, and Cowdry inclusions herpesviruses.