MicroRNAs in Penile Cancer: Challenges, Opportunities, and Translational Perspectives

A Brazilian review catalogs miRNAs tied to penile cancer progression and HPV status — but the underlying studies are nearly all too small and descriptive to act on

Journal: Critical Reviews in Oncology/Hematology | Published: 2026-03-13 | Type: Review | PMID: 41833893 Authors: Furuya TK, Carrasco AG, Uno M, et al. — Center for Translational Research in Oncology (LIM24), Instituto do Câncer do Estado de São Paulo (ICESP/HCFMUSP), São Paulo, Brazil Funding/COI: Funding not disclosed. Authors declare no competing interests.

Summary

Penile cancer is rare globally but disproportionately burdens men in parts of South America, Africa, and Asia where HPV vaccination and circumcision rates are low. This review from a major Brazilian cancer center catalogs what's known about microRNAs (miRNAs) — small non-coding RNA molecules that regulate gene expression — as potential biomarkers for diagnosing, staging, and treating penile cancer. The authors find the field nascent and the evidence thin: most existing studies are descriptive surveys of which miRNAs are up or downregulated, with little mechanistic work and almost no clinical validation.

Claims

• Multiple miRNAs are differentially expressed in penile cancer tissue versus normal tissue, with some correlating with tumor aggressiveness and HPV infection status
• Several miRNAs show association with patient prognosis, though the review's abstract does not quantify specific miRNAs, effect sizes, or hazard ratios
• Geographic disparities are pronounced: most miRNA research in penile cancer originates from a handful of countries, while high-incidence regions (sub-Saharan Africa, parts of South America) are underrepresented in the evidence base
• Extracellular vesicles (EVs) — cell-released nanoparticles circulating in blood — are identified as an emerging non-invasive source for detecting circulating miRNAs
• Multi-omics integration and AI-assisted analysis are proposed as tools to accelerate biomarker validation

Study Quality

This is a narrative review, not a systematic review or meta-analysis. The authors describe performing a "comprehensive review of published studies" but the abstract reports no PRISMA flow diagram, formal search strategy, or explicit inclusion/exclusion criteria. Without a structured protocol, selection bias is a live concern — narrative reviews are susceptible to unconscious framing of the literature.

The authors are frank about the underlying literature's limits: they acknowledge that most source studies feature small cohorts and lack functional validation. That means the candidate miRNAs identified haven't been shown to mechanistically drive cancer biology — they're correlations. This candor is a mark in the paper's favor, but it also defines the ceiling on what conclusions the review can support. No pooled effect sizes or heterogeneity analyses are possible given the state of the field.

Red Flags

• Narrative review design — no systematic search strategy or PRISMA reported; inherently susceptible to selection bias
• Funding source not disclosed; unclear whether pharmaceutical or device industry support was involved
• No quantitative synthesis — no pooled effect sizes, confidence intervals, or heterogeneity assessment
• The source literature is self-described as dominated by small, descriptive cohort studies with no functional validation
• High-incidence populations — where this disease causes the most harm — are barely represented in the evidence base
• No specific miRNA names, effect sizes, or hazard ratios appear in the abstract; the review may catalog findings without synthesizing them into actionable signals

Strengths

• ICESP/HCFMUSP is one of Brazil's leading cancer centers; the authors have firsthand clinical exposure to a disease Brazil sees at higher rates than most Western countries
• Raises the geographic disparity issue explicitly — a legitimate research priority call
• Covers emerging platforms (high-throughput sequencing, bioinformatics, extracellular vesicles) alongside established approaches
• No declared conflicts of interest

Verdict

This review maps the miRNA landscape in penile cancer, a malignancy so rare in wealthy countries that it rarely attracts sustained research investment. The most important finding is tucked into the authors' own candid assessment: virtually all existing studies are too small and too descriptive to support clinical use. That's not a criticism of this paper — it's an accurate characterization of the field. For researchers working in penile cancer or rare oncology, it's a useful survey of where the science stands and where the gaps are. For everyone else, it illustrates a chronic problem in rare cancers: the disease is too uncommon to recruit large trials, which means even promising biomarker leads can take decades to validate.