Ehvidence
Favorable Efficacy (RCT)

Oral retinol for skin cancer prevention

Oral retinol (vitamin A) 25,000 IU daily vs. Placebo · for Skin cancer (moderate-risk) · real-time analysis of 1 studies · updated 2026-05-29

In moderate-risk people with extensive actinic damage, high-dose oral retinol modestly reduced squamous-cell carcinoma but had no effect on basal-cell carcinoma.

Efficacy (RCT): Efficacy evidence on clinical outcomes. Effects are risk ratios with number-needed-to-treat where a baseline risk is available. Glossary →

Interpretation & tips

Benefit was modest and specific to squamous-cell carcinoma; basal-cell was unaffected. High-dose vitamin A carries toxicity (hepatic, teratogenic) that limits routine use.

26% lower risk of squamous-cell carcinoma
Pooled RR 0.74 (95% CI 0.56–0.98) across 1 studies, 2,297 patients (random-effects, I² 0%).
0.74
Pooled RR
0.56–0.98
95% CI
1
Studies
2,297
Patients
—
NNT

Forest plot—Squamous-cell carcinoma

SKICAP-AK (Moon) 1997 0.74 [0.56–0.99] Pooled (RE) 0.74 [0.56–0.98] 0.1 0.25 0.5 1 2 4 ← favors treatment favors control →

Study results—Squamous-cell carcinoma

Study Design Dose / regimen Treatment Control RR [95% CI] Improvement NNT Weight
SKICAP-AK (Moon) 1997 note RCT Retinol 25,000 IU/day — — 0.74 [0.56–0.99] ~ 26% — 100%

RR < 1 favors treatment for outcomes where lower is better. Rows in gray have a confidence interval crossing 1 (individually inconclusive). “~” marks effects reported as OR/HR and treated as RR-approximations. “excl” = excluded from pooling (e.g. reviews).

Notes & interpretation

  • SKICAP-AK (Moon) 1997—First new squamous-cell carcinoma.

Background

The SKICAP-AK trial randomized 2,297 people with a history of many actinic keratoses (and ≤2 prior skin cancers) to retinol 25,000 IU daily or placebo, with a median 3.8 years of follow-up.

Topic methodology & caveats

Published hazard ratios with 95% CIs; no control risk encoded, so NNT is not shown. Single trial.

Studies