Verification note (2026-05-19): Canonical-DB metadata verified against PubMed efetch (PMID 29704456) and Crossref. n=24 women (48 forearms), pages 1819-1826, volume 32 issue 10 are confirmed correct. Prior seeding brief cited n=60 and pages 1734-1741 — those values are wrong for this DOI and have been corrected. The paper is closed-access (not_oa); no local PDF is available. All quantitative claims beyond what the PubMed abstract states are tagged #gap/no-fulltext-access and remain unverifiable until PDF access is obtained. See verified-scope in frontmatter for full scope.

Tretinoin (0.05% cream vs. 5% peel) for photoaging and field cancerization of the forearms: randomized, evaluator-blinded, clinical trial

Sumita JM et al. · J Eur Acad Dermatol Venereol 32(10):1819-1826 · 2018 · DOI: 10.1111/jdv.15020

TL;DR

A randomized, evaluator-blinded RCT in 24 women (48 forearms, bilateral within-person design) comparing 0.05% tretinoin cream (applied three nights per week) against 5% tretinoin peel (applied every two weeks) for photoaging and field cancerization of the forearms. Both formulations produced comparable reductions in photoaging scores (~20%) and actinic keratosis (AK) counts (~60% from baseline) no-fulltext-access. However, they diverged on three secondary endpoints: corneal layer thickness, dermis echogenicity, and Ki67 immunohistochemistry showed opposite directional changes between the two arms. The cream was superior on ultrasonographic aging markers; the peel was superior for stabilizing field cancerization. Both demonstrated good tolerability. This study is cited in the photoaging literature as evidence that topical tretinoin reduces actinic damage and supports genomic-instability reversal in field-cancerized skin.

Background

Topical tretinoin (all-trans retinoic acid) is the best-characterized pharmacological intervention for photoaged skin. Its mechanism operates through nuclear retinoic acid receptors (RARs), which regulate gene expression to promote collagen synthesis, reduce matrix metalloproteinase (MMP) activity, increase epidermal thickness, and suppress UV-induced apoptosis resistance. In chronically sun-damaged skin, tretinoin also reduces markers of field cancerization — the molecular abnormalization of an epithelial field that precedes frank malignancy.

By 2018, topical tretinoin cream (0.05–0.1%) had an established evidence base for photoaging reversal, but the relative efficacy and tissue-level effects of low-concentration cream versus high-concentration peel formulations had not been systematically compared in an RCT with objective histological and ultrasonographic endpoints ¹.

Molecularly, tretinoin modulates key aging-associated processes in UV-exposed skin: it downregulates p53-pathway abnormalities accumulated via UV mutagenesis, increases Ki67-indexed epidermal proliferation (tissue repopulation), and alters extracellular matrix composition in the dermis. These endpoints — p53 IHC, bcl-2 IHC, Ki67 IHC, collagen I IHC, and ultrasound-based dermis echogenicity — were included as secondary outcomes, providing a mechanistic window into the genomic-instability hallmark in skin aging. no-fulltext-access

Methods

Study design: Randomized, evaluator-blinded clinical trial (one-sided within-person crossover-adjacent design — each participant’s two forearms received different treatments, eliminating inter-individual variation). no-fulltext-access — full randomization procedures, allocation concealment, and blinding details not verifiable without primary PDF.

Population: 24 women enrolled, age >60 years, Fitzpatrick phototypes II-III, with photoaging of the forearms; additionally specified as not having undergone hormone replacement therapy (confirmed from PubMed abstract Methods text). One participant dropped out; per-protocol analysis n=23 (46 forearms). no-fulltext-access — exclusion criteria, baseline demographics, and Fitzpatrick distribution details not available from abstract.

Interventions:

• Arm A (cream): 0.05% tretinoin cream, applied to one forearm three nights per week
• Arm B (peel): 5% tretinoin peel, applied to the other forearm every two weeks

Treatment duration not confirmed from abstract — no-fulltext-access.

Outcome assessments: The abstract and MeSH terms indicate the following endpoints were measured (verifier should confirm assessment schedule and primary vs secondary designation from full text): no-fulltext-access

Modality	Marker
Clinical scoring	Photoaging severity scale (quantitative)
Clinical counting	Actinic keratosis lesion count
Ultrasound	Dermis echogenicity; corneal layer thickness
Corneometry	Skin hydration
Profilometry	Surface texture
Histology	Collagen I (dermis)
IHC	p53, bcl-2, Ki67

Preregistration: No trial registration number identified in PubMed record or ClinicalTrials.gov query. no-fulltext-access — it is possible a Brazilian registry (ReBEC) registration exists that was not indexed.

Findings

All quantitative claims below derive from PubMed abstract only. Verify against primary PDF before relying on exact figures. no-fulltext-access

Primary efficacy: comparable between arms

Both 0.05% cream and 5% peel produced ¹:

• ~20% reduction in photoaging scores from baseline — effect size comparable between arms
• ~60% reduction in actinic keratosis counts from baseline — effect size comparable between arms

Whether these reductions were statistically significant versus each other or versus a no-treatment control is not stated in the abstract; the study was powered to detect between-arm differences rather than testing against an untreated control. no-fulltext-access

Secondary endpoints: divergent directional effects

Three endpoints showed opposite effects between the two arms, each at P < 0.05 (confirmed from PubMed abstract) ¹:

1. Corneal layer thickness: decreased with 0.05% cream; increased with 5% peel
2. Dermis echogenicity (ultrasound): increased with 0.05% cream (consistent with collagen remodeling / improved dermis density); decreased with 5% peel
3. Ki67 expression (proliferation marker): increased with 0.05% cream; decreased with 5% peel

The directional divergence on dermis echogenicity is notable: in the aging-biology context, increased dermis echogenicity is generally interpreted as improved extracellular matrix integrity (consistent with collagen synthesis promotion by tretinoin). The cream’s superior ultrasonographic result suggests deeper dermal remodeling via the cream formulation, despite the lower tretinoin concentration. The peel’s lower dermis echogenicity may reflect transient post-peel dermal reorganization or a different phase of tissue response. no-fulltext-access — mechanistic interpretation requires full histology and IHC data from the primary PDF.

Formulation-specific advantages

• Cream superior for: ultrasonographic aging markers (dermis echogenicity improvement) no-fulltext-access
• Peel superior for: field cancerization stabilization (AK reduction / Ki67 pattern consistent with normalized proliferation in pre-cancerous field) no-fulltext-access

Safety and tolerability

Both regimens demonstrated good tolerability in the abstract summary. Specific adverse event rates, types (erythema, peeling, desquamation), and severity grading are not available from the abstract. no-fulltext-access

Relevance to the genomic-instability hallmark

This study tests an intervention on actinic keratosis burden — a direct measure of genomic-instability accumulation in UV-exposed epithelium. Actinic keratoses arise from p53-mutant keratinocytes that have sustained UV-induced DNA damage and survived via disrupted apoptosis (bcl-2 upregulation, p53 mutation). The ~60% reduction in AK count by both formulations represents partial reversal of a field-cancerized genomic landscape.

The IHC endpoints (p53, bcl-2, Ki67) directly address genomic-instability and its cellular consequences, though the specific directional changes in these markers are not reported in the abstract. no-fulltext-access

Mechanistically, tretinoin promotes:

• Increased keratinocyte turnover (Ki67-mediated proliferation, diluting mutant clones)
• Upregulation of collagen synthesis and downregulation of MMP activity
• Restoration of RAR-mediated transcription disrupted by UV

The inclusion of p53 and bcl-2 IHC endpoints positions this study as mechanistically relevant to both genomic-instability (p53 mutation burden in field) and the apoptosis-evasion component that enables field cancerization to persist.

Extrapolation

This is a fully human RCT; no model-organism extrapolation required.

Dimension	Status
Pathway conserved in humans?	N/A (direct human study)
Phenotype conserved in humans?	N/A (direct human study)
Replicated in humans?	yes — tretinoin for photoaging; this paper provides formulation-comparison data

Limitations

• Closed access / no fulltext verification: All quantitative claims in this page are from abstract only. Specific effect sizes (CIs, p-values), statistical methods, and secondary endpoint details require the primary PDF. no-fulltext-access
• n=24 (48 forearms): Small sample. Confidence intervals on the 20% photoaging and 60% AK reduction figures are not available but are likely wide. no-fulltext-access
• Women only; Fitzpatrick II-III only: Results may not generalize to men, darker skin types, or other body sites.
• Bilateral within-person design with active treatments in both arms: Lack of an untreated control forearm means both arms are compared to each other and to their own baseline, not to a no-treatment control. Spontaneous regression of AKs or regression-to-the-mean cannot be fully excluded without a placebo arm.
• Forearm vs face: Photoaging and field cancerization of the forearm may differ in baseline severity, skin thickness, and treatment-response kinetics from the face (the more common cosmetic concern). Generalizability to facial photoaging is not established by this study.
• Peel concentration (5%): The 5% tretinoin peel concentration is substantially higher than the cream (0.05%). Whether the divergent results reflect the formulation vehicle, the concentration difference, or the application frequency difference (continuous vs intermittent) cannot be disentangled.
• Seeding-brief metadata error — resolved (2026-05-19): Seeding brief cited n=60 and pages 1734-1741; PubMed (PMID 29704456) and Crossref both return n=24 women (48 forearms) and pages 1819-1826 for DOI 10.1111/jdv.15020. Canonical-DB values are confirmed correct. The n=60 and pages 1734-1741 figures in the seeding brief do not correspond to this DOI; they may refer to a different paper. All downstream citations (see phenotypes/skin-aging.md footnote [^sumita2018]) must be updated to n=24 and pages 1819-1826.
• No preregistration identified. Registration in a Brazilian-national registry (ReBEC) cannot be excluded but was not found in PubMed indexing or ClinicalTrials.gov search.

Limitations and gaps

no-fulltext-access — entire quantitative extraction is abstract-only; primary PDF required for verification
needs-replication — single small RCT (n=24); independent replication needed before endpoint claims are treated as robust
dose-response-unclear — cream (0.05%) vs peel (5%) differs in both vehicle and concentration; the concentration-response relationship for these endpoints is not established by this design
long-term-unknown — treatment duration and follow-up period not available from abstract; long-term durability of AK reduction unknown

Cross-references

This study provides human evidence relevant to:

• tretinoin — canonical home for mechanism, dose-response, clinical-stage data; this study provides formulation-comparison RCT data (R41 forward-ref — tretinoin compound page not yet seeded)
• genomic-instability — AK reduction as direct measure of field-cancerization reversal; p53/bcl-2 IHC endpoints
• sasp — field cancerization involves senescence-associated secretory phenotype in pre-malignant keratinocytes; tretinoin effects on SASP in this context not addressed by the study
• cancer — actinic keratosis as squamous cell carcinoma precursor; field cancerization endpoint is clinically meaningful

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Footnotes

1. sumita-2018-tretinoin-photoaging · n=24 enrolled (23 per-protocol; 1 dropout) · 48 forearms, bilateral within-person design · rct · evaluator-blinded · mean 20% reduction in photoaging score and 60% reduction in AK count (no between-arm difference); three endpoints diverged between arms at P<0.05 (corneal thickness, dermis echogenicity, Ki67) — cream superior ultrasonographic markers; peel superior field cancerization · model: human (forearm, Fitzpatrick II-III, women >60 yr, no HRT) · doi:10.1111/jdv.15020 · PMID 29704456 · J Eur Acad Dermatol Venereol 2018;32(10):1819-1826 · closed access; body claims are abstract-only no-fulltext-access ↩ ↩² ↩³