🧬A Tapeworm That Turned Malignant: Hymenolepis nana Mimicking Cancer in an HIV Patient

FRCPath Prep Medical Microbiology Consultants
Jul 30
2 min read

Published: 29 July 2025

Category: Parasitology | Rare Case | FRCPath Spotter

🔎 What Happened?

A 41-year-old man with untreated HIV in Colombia died from widespread masses in his lungs and lymph nodes. Doctors initially thought it was cancer, but lab tests showed something strange:

The tumor cells were too small to be human.
They came from a tapeworm parasite — specifically, Hymenolepis nana.
These parasite cells had become cancer-like and invaded the patient’s organs.

This was the first recorded case of cancer from a parasite’s own cells growing inside a human.

🦠 What Is Hymenolepis nana?

Feature	Details
Common name	Dwarf tapeworm
Transmission	Feco-oral; autoinfection possible
Normal infection site	Small intestine
Unique feature	Can complete its life cycle in 1 host
At-risk population	Children, immunocompromised patients

🧪 Key Lab Findings

Investigation	Result
Histology	Tiny, fast-growing, cancer-like cells
Broad-range PCR	DNA from H. nana
In situ hybridization	Parasite DNA in tumor tissue, not human DNA
Genetic sequencing	Cancer-like mutations in parasite DNA

📌 Why This Case Matters

New disease mechanism: Not human cancer, but a tapeworm's cells turning cancerous.
Happened in a severely immunosuppressed patient.
Important FRCPath lesson: Always consider parasites in unusual histology, especially in immunocompromised patients.

🧠 For FRCPath Part 2: Spotter / OSPE

Clue	Interpretation
Small tumor cells, too small for human	Think: parasite origin
Negative for human DNA, positive for cestode DNA	Suggests non-human source
Immunocompromised host	Increased risk of unusual infections
Molecular tools used	Broad PCR, sequencing, in situ hybridization

⚠️ Take-Home Message

Hymenolepis nana can rarely behave like a cancer in humans — but only the parasite’s own cells grow uncontrollably.
The case shows the power of molecular diagnostics to solve medical mysteries.
Stay alert in exams for rare host–parasite interactions, especially in HIV patients.