Distinct roles of SOX9 in self-renewal of progenitors and mesenchymal transition of the endothelium.

Regenerative capabilities of the endothelium rely on vessel-resident progenitors termed endothelial colony forming cells (ECFCs). This study aimed to investigate if these progenitors are impacted by conditions (i.e., obesity or atherosclerosis) characterized by increased serum levels of oxidized low-density lipoprotein (oxLDL), a known inducer of Endothelial-to-Mesenchymal Transition (EndMT). Our investigation focused on understanding the effects of EndMT on the self-renewal capabilities of progenitors and the associated molecular alterations. In the presence of oxLDL, ECFCs displayed classical features of EndMT, through reduced endothelial gene and protein expression, function as well as increased mesenchymal genes, contractility, and motility. Additionally, ECFCs displayed a dramatic loss in self-renewal capacity in the presence of oxLDL. RNA-sequencing analysis of ECFCs exposed to oxLDL validated gene expression changes suggesting EndMT and identified SOX9 as one of the highly differentially expressed genes. ATAC sequencing analysis identified SOX9 binding sites associated with regions of dynamic chromosome accessibility resulting from oxLDL exposure, further pointing to its importance. EndMT phenotype and gene expression changes induced by oxLDL in vitro or high fat diet (HFD) in vivo were reversed by the silencing of SOX9 in ECFCs or the endothelial-specific conditional knockout of Sox9 in murine models. Overall, our findings support that EndMT affects vessel-resident endothelial progenitor's self-renewal. SOX9 activation is an early transcriptional event that drives the mesenchymal transition of endothelial progenitor cells. The identification of the molecular network driving EndMT in vessel-resident endothelial progenitors presents a new avenue in understanding and preventing a range of condition where this process is involved.

Development of Physiologically Relevant Skin Organoids from Human Induced Pluripotent Stem Cells.

The development of skin organs for studying developmental pathways, modeling diseases, or regenerative medicine purposes is a major endeavor in the field. Human induced pluripotent stem cells (hiPSCs) are successfully used to derive skin cells, but the field is still far from meeting the goal of creating skin containing appendages, such as hair follicles and sweat glands. Here, the goal is to generate skin organoids (SKOs) from human skin fibroblast or placental CD34+ cell-derived hiPSCs. With all three hiPSC lines, complex SKOs with stratified skin layers and pigmented hair follicles are generated with different efficacies. In addition, the hiPSC-derived SKOs develop sebaceous glands, touch-receptive Merkel cells, and more importantly eccrine sweat glands. Together, physiologically relevant skin organoids are developed by direct induction of embryoid body formation, along with simultaneous inactivation of transforming growth factor beta signaling, activation of fibroblast growth factor signaling, and inhibition of bone morphogenetic protein signaling pathways. The skin organoids created in this study can be used as valuable platforms for further research into human skin development, disease modeling, or reconstructive surgeries.

Lymphatic expression of the proliferation marker Ki67 is linked to sentinel node positivity, recurrence and mortality in primary cutaneous melanoma.

Lymphangiogenesis is a precursor to lymphovascular invasion, and may therefore signal a higher risk of metastasis and mortality in primary cutaneous melanoma. This retrospective longitudinal study aimed to evaluate whether emergent lymphangiogenesis, as measured through co-expression of endothelial proteins with the proliferation marker Ki67, was associated with poorer prognosis in a cohort of patients with single primary cutaneous melanoma. We screened all patients with a single locally invasive primary cutaneous melanoma who received sentinel lymph node biopsy at a tertiary dermatology centre in Brisbane, Australia between 1994 and 2007. Primary melanoma sections were stained via Opal multiplex immunofluorescence, and categorized according to the presence of Ki67 within either CD31+ or D2-40+ endothelial cells. Multivariate Cox regression modelling was used to evaluate associations between endothelial Ki67 positivity and clinical outcomes, with adjustment for age, sex, Breslow depth, ulceration, and anatomical location. Overall, 264 patients were available for analysis, with a median follow-up duration of 7.1 years. The presence of D2-40+ /Ki67+ co-expression was associated with greater melanoma-specific mortality (adjusted hazard ratio [HR]: 2.03; 95% confidence interval [CI]: 1.33-3.10; p = 0.001) and recurrence (adjusted HR: 1.70; 95% CI: 1.33-3.10; p = 0.001) relative to absence. CD31+ /Ki67+ co-expression was not prognostic in this cohort. Lymphatic proliferation, as measured through D2-40+ /Ki67+ co-expression, predicted greater melanoma-specific mortality and recurrence in this cohort of primary cutaneous melanoma.

Germline variants are associated with increased primary melanoma tumor thickness at diagnosis.

Germline genetic variants have been identified, which predispose individuals and families to develop melanoma. Tumor thickness is the strongest predictor of outcome for clinically localized primary melanoma patients. We sought to determine whether there is a heritable genetic contribution to variation in tumor thickness. If confirmed, this will justify the search for specific genetic variants influencing tumor thickness. To address this, we estimated the proportion of variation in tumor thickness attributable to genome-wide genetic variation (variant-based heritability) using unrelated patients with measured primary cutaneous melanoma thickness. As a secondary analysis, we conducted a genome-wide association study (GWAS) of tumor thickness. The analyses utilized 10 604 individuals with primary cutaneous melanoma drawn from nine GWAS datasets from eight cohorts recruited from the general population, primary care and melanoma treatment centers. Following quality control and filtering to unrelated individuals with study phenotypes, 8125 patients were used in the primary analysis to test whether tumor thickness is heritable. An expanded set of 8505 individuals (47.6% female) were analyzed for the secondary GWAS meta-analysis. Analyses were adjusted for participant age, sex, cohort and ancestry. We found that 26.6% (SE 11.9%, P = 0.0128) of variation in tumor thickness is attributable to genome-wide genetic variation. While requiring replication, a chromosome 11 locus was associated (P < 5 × 10-8) with tumor thickness. Our work indicates that sufficiently large datasets will enable the discovery of genetic variants associated with greater tumor thickness, and this will lead to the identification of host biological processes influencing melanoma growth and invasion.

The role of dermocosmetics in the management of cancer-related skin toxicities: international expert consensus.

Skin toxicities are very common in patients undergoing cancer treatment and have been found to occur with all types of cancer therapeutic interventions (cytotoxic chemotherapy, targeted therapies, immunotherapy, and radiotherapy). Further, skin toxicities can lead to interruption or even discontinuation of anticancer treatment in some patients, translating to suboptimal outcomes. Dermocosmetics (or cosmeceuticals)-defined as skincare solutions incorporating dermatologically active ingredients (beyond vehicle effects) that directly improve symptoms of various skin conditions-are increasingly being used in cancer care to prevent and manage skin toxicities. The active ingredients in these products have a measurable biological action in skin; they typically improve skin integrity (barrier function/hydration and other factors) while relieving skin symptoms. The Association Francophone des Soins Oncologiques de Support (AFSOS) and Multinational Association of Supportive Care in Cancer (MASCC) partnered to select a multidisciplinary group of healthcare professionals involved in the management of patients with cancer and skin toxicities. The group reviewed existing literature and created a summary of recommendations for managing these toxicities through online meetings and communication. In this publication, the group (1) reviews new skin toxicities seen with oncology drugs and (2) evaluates the role of dermocosmetics in improving patient outcomes and minimizing cancer treatment interruptions. We provide general recommendations for initiation and selection of skin care in all oncology patients as well as recommendations for what factors should be considered when using dermocosmetics in specific types of skin toxicities.

Conditional survival in patients with stage IB-IIIA melanoma undergoing sentinel node biopsy in Queensland: A longitudinal study.

BACKGROUND: Tumour characteristics such as thickness and ulceration, along with sentinel lymph node (SLN) status, have been essential in predicting survival in patients with locally invasive melanomas at the time of diagnosis. It is unclear if these prognostic factors are relevant 1, 2 or 5 years after diagnosis. OBJECTIVES: The key aim of this project was to analyse conditional survival in a cohort of Queensland patients with stage IB to IIIA melanomas (American Joint Committee on Cancer's staging system, 8th version) and to test the relevance of clinicopathological prognostic factors for melanoma outcome after varying intervals of survival time. METHODS: Patients with primary invasive cutaneous melanoma who were referred to a tertiary melanoma clinic and underwent SLN biopsy between 1994 and 2011 were ascertained. The effect of patient and tumour characteristics on melanoma survival were calculated using multivariate Cox proportional hazard models at diagnosis and at variable times after diagnosis. RESULTS: The final analysis included 651 patients (average age 49 years, 55.5% male) with stage IB to IIIA melanoma. At diagnosis, and after 1 and 2 years survived, SLN positivity, thickness and ulceration were predictive of 10-year survival since diagnosis. However, once patients survived 5 years, only SLN status was predictive. Overall conditional melanoma survival improved with increasing time survived. Five years after diagnosis, 10-year conditional melanoma survival (MSS) was 91% (95% CI 86%-95%) compared with 85% (82%-88%) predicted at diagnosis. The improvement in MSS was observed mainly for Stage II melanoma patients and not for those with a positive SLN biopsy. CONCLUSIONS: This study confirms the improvement of prognosis according to time survived since diagnosis suggesting that after 5 years survival the classic prognostic indicators may not have the same influence.

Patterns and cost of care according to keratinocyte cancer risk stratification in a volunteer population screening clinic: Real-world data from the TRoPICS study.

BACKGROUND: Risk prediction tools have been developed for keratinocyte cancers (KCs) to effectively categorize individuals with different levels of skin cancer burden. Few have been clinically validated nor routinely used in clinical settings. OBJECTIVES: To assess whether risk prediction tool categories associate with interventions including chemoprophylaxis for skin cancer, and health-care costs in a dermatologist-run screening clinic. METHODS: Adult participants who presented to a walk-in screening facility were invited to participate. A self-completed KC risk prediction tool was used to classify participants into one of the five risk categories. Participants subsequently underwent full skin examination by a dermatologist. Dermatological interventions and skin cancer-related medical prescriptions were documented. Total health-care costs, both to the health-care system and patients were evaluated. RESULTS: Of the 507 participants recruited, 5-fluorouracil cream and nicotinamide were more frequently prescribed in the higher risk groups as chemoprophylaxis (p < 0.005). A significant association with high predicted risk was also observed in the use of cryotherapy and curettage and cautery (p < 0.05). The average health-care costs associated with a skin check visit increased from $90 ± 37 (standard deviation) in the lowest risk group to $149 ± 97 in the highest risk group (p < 0.0001). CONCLUSIONS: We observed a positive association between higher predicted risk of skin cancer and the prescription of chemoprophylaxis and health-care costs involved with opportunistic community skin cancer screening. A clinical use of risk stratification may be to provide an opportunity for clinicians to discuss skin cancer prevention and chemoprophylaxis with individual patients.

Hypothesised cutaneous sites of origin of stage III melanomas with unknown primary: A multicentre study.

Based on molecular evidence that melanomas with unknown primary (MUPs) arise from the skin, we hypothesised that sites of MUPs are disproportionately on trunk and lower limbs, sites that are not readily visible to patients and clinicians. We tested this hypothesis by inferring the anatomic site of origin of MUPs from the corresponding known cutaneous sites of melanoma patients with known primary tumours (MKPs). We analysed data from three separate cohorts of patients from Brisbane, Australia (n = 236); Manchester, UK (n = 51) and Padova, Italy (n = 33), respectively, who first presented with stage III melanoma with lymph node metastases. We matched two MKP patients to each MUP patient based on lymph node dissection (LND) site, age and sex, and imputed cutaneous sites of origin of MUPs from their two matched MKPs for study countries, giving two possible sites for each MUP per centre. Overall, results showed that MUP patients were predominantly male, and trunk was the most likely origin, comprising around a third to a half of MUPs across the three cohorts. The remaining MUP inferred sites varied by country. In the Australian cohort, the legs accounted for a third of imputed sites of MUPs, while in the UK and Italian cohorts, the most frequent site was the arms followed by the legs. Our findings suggest the need for regular and thorough skin examination on trunk and limbs, especially in males, to improve early detection of cutaneous melanoma and reduce the risk of metastatic disease at the time of presentation.

Multiplex melanoma families are enriched for polygenic risk.

Cancers, including cutaneous melanoma, can cluster in families. In addition to environmental etiological factors such as ultraviolet radiation, cutaneous melanoma has a strong genetic component. Genetic risks for cutaneous melanoma range from rare, high-penetrance mutations to common, low-penetrance variants. Known high-penetrance mutations account for only about half of all densely affected cutaneous melanoma families, and the causes of familial clustering in the remainder are unknown. We hypothesize that some clustering is due to the cumulative effect of a large number of variants of individually small effect. Common, low-penetrance genetic risk variants can be combined into polygenic risk scores. We used a polygenic risk score for cutaneous melanoma to compare families without known high-penetrance mutations with unrelated melanoma cases and melanoma-free controls. Family members had significantly higher mean polygenic load for cutaneous melanoma than unrelated cases or melanoma-free healthy controls (Bonferroni-corrected t-test P = 1.5 × 10-5 and 6.3 × 10-45, respectively). Whole genome sequencing of germline DNA from 51 members of 21 families with low polygenic risk for melanoma identified a CDKN2A p.G101W mutation in a single family but no other candidate high-penetrance melanoma susceptibility genes. This work provides further evidence that melanoma, like many other common complex disorders, can arise from the joint action of multiple predisposing factors, including rare high-penetrance mutations, as well as via a combination of large numbers of alleles of small effect.

Resident vascular endothelial progenitor definition and function: the age of reckoning.

The cardiovascular system is composed around the central function of the endothelium that lines the inner surfaces of its vessels. In recent years, the existence of a progenitor population within the endothelium has been validated through the study of endothelial colony-forming cells (ECFCs) in human peripheral blood and certain vascular beds. However, our knowledge on endothelial populations in vivo that can give rise to ECFCs in culture has been limited. In this review we report and analyse recent attempts at describing progenitor populations in vivo from murine studies that reflect the self-renewal and stemness capacity observed in ECFCs. We pinpoint seminal discoveries within the field, which have phenotypically defined, and functionally scrutinised these endothelial progenitors. Furthermore, we review recent publications utilising single-cell sequencing technologies to better understand the endothelium in homeostasis and pathology.

Pathways from Diagnosis to Death from Keratinocyte Cancer in Kidney Transplant Recipients.

BACKGROUND: Kidney transplant recipients are at increased risk of developing and dying from keratinocyte cancer. We aimed to describe the clinical course of keratinocyte cancer-related deaths in a cohort of kidney transplant recipients. METHODS: In kidney transplant recipients transplanted between 1995 and 2014 in Queensland, Australia, we ascertained keratinocyte cancer deaths by searching national transplant and state death registries to March 2020. Deceased transplant recipients' medical records were reviewed to assess features of the primary lesion of the fatal keratinocyte cancer, metastases, and clinical information before death. RESULTS: Of 658 kidney transplant recipient deaths, 49 (7%) were due to keratinocyte cancer, and medical records were available for 36 (73%). One death was due to basal cell carcinoma, and 35 were from squamous cell carcinoma (SCC), primarily from the head and neck (24; 69%). The most common site of metastasis was the lungs (21; 58%). Median time (minimum, maximum) from the diagnosis of primary SCC to metastasis was 5 months (0, 29). After this, the median time to death was 9 months (1, 50). CONCLUSION: Fatal keratinocyte cancers overwhelmingly arise on the head and neck, with lungs the most common metastasis site. The short time from diagnosis of primary to death indicates the aggressive nature of these keratinocyte cancers.

Forever Connected: The Lifelong Biological Consequences of Fetomaternal and Maternofetal Microchimerism.

BACKGROUND: Originally studied as a mechanism to understand eclampsia-related deaths during pregnancy, fetal cells in maternal blood have more recently garnered attention as a noninvasive source of fetal material for prenatal testing. In the 21st century, however, intact fetal cells have been largely supplanted by circulating cell-free placental DNA for aneuploidy screening. Instead, interest has pivoted to the ways in which fetal cells influence maternal biology. In parallel, an increasing appreciation of the consequences of maternal cells in the developing fetus has occurred. CONTENT: In this review, we highlight the potential clinical applications and functional consequences of the bidirectional trafficking of intact cells between a pregnant woman and her fetus. Fetal cells play a potential role in the pathogenesis of maternal disease and tissue repair. Maternal cells play an essential role in educating the fetal immune system and as a factor in transplant acceptance. Naturally occurring maternal microchimerism is also being explored as a source of hematopoietic stem cells for transplant in fetal hematopoietic disorders. SUMMARY: Future investigations in humans need to include complete pregnancy histories to understand maternal health and transplant success or failure. Animal models are useful to understand the mechanisms underlying fetal wound healing and/or repair associated with maternal injury and inflammation. The lifelong consequences of the exchange of cells between a mother and her child are profound and have many applications in development, health, and disease. This intricate exchange of genetically foreign cells creates a permanent connection that contributes to the survival of both individuals.

Long-term deaths from melanoma according to tumor thickness at diagnosis.

There is little long-term follow-up information about how the number of melanoma deaths and case fatality vary over time according to the measured thickness of melanoma at diagnosis. This population-based longitudinal cohort study examines patterns and trends in case fatality among 44,531 people in Queensland (Australia) diagnosed with a single invasive melanoma (International Classification of Diseases for Oncology, third revision [ICD-O-3], C44, Morphology 872-879) between 1987 and 2011, including 11,883 diagnosed between 1987 and 1996, with up to 20 years follow-up (to December 2016). The 20-year case fatality increased by thickness, with the percentage of melanoma deaths within 20 years of diagnosis being up to 4.8% for melanomas with measured thickness <0.80 mm, 10.6% for tumors 0.8 to <1.0 mm and generally more than 30% for melanomas measuring 3 mm and more. For melanomas <1.0 mm, most deaths occurred between 5 and 20 years after diagnosis, whereas for thicker melanomas the reverse was true with most deaths occurring within the first 5 years. Five-year case fatality decreased over successive calendar time periods for melanomas <1.0 mm, but not for melanomas ≥1.0 mm. These findings demonstrate that the time course for fatal melanomas varies markedly according to tumor thickness at diagnosis. Improved understanding of the patient factors and characteristics of melanomas, in addition to tumor thickness, which increase the likelihood of progression, is needed to guide clinical diagnosis, communication with patients and ongoing surveillance pathways of patients with potentially fatal lesions.

Bimodal behaviour of interfollicular epidermal progenitors regulated by hair follicle position and cycling.

Interfollicular epidermal (IFE) homeostasis is a major physiological process allowing maintenance of the skin barrier function. Despite progress in our understanding of stem cell populations in different hair follicle compartments, cellular mechanisms of IFE maintenance, in particular, whether a hierarchy of progenitors exists within this compartment, have remained controversial. We here used multicolour lineage tracing with Brainbow transgenic labels activated in the epidermis to track individual keratinocyte clones. Two modes of clonal progression could be observed in the adult murine dorsal skin. Clones attached to hair follicles showed rapid increase in size during the growth phase of the hair cycle. On the other hand, clones distant from hair follicles were slow cycling, but could be mobilized by a proliferative stimulus. Reinforced by mathematical modelling, these data support a model where progenitor cycling characteristics are differentially regulated in areas surrounding or away from growing hair follicles. Thus, while IFE progenitors follow a non-hierarchical mode of development, spatiotemporal control by their environment can change their potentialities, with far-reaching implications for epidermal homeostasis, wound repair and cancer development.

Dominant-negative Sox18 function inhibits dermal papilla maturation and differentiation in all murine hair types.

SOX family proteins SOX2 and SOX18 have been reported as being essential in determining hair follicle type; however, the role they play during development remains unclear. Here, we demonstrate that Sox18 regulates the normal differentiation of the dermal papilla of all hair types. In guard (primary) hair dermal condensate (DC) cells, we identified transient Sox18 in addition to SOX2 expression at E14.5, which allowed fate tracing of primary DC cells until birth. Similarly, expression of Sox18 was detected in the DC cells of secondary hairs at E16.5 and in tertiary hair at E18.5. Dominant-negative Sox18 mutation (opposum) did not prevent DC formation in any hair type. However, it affected dermal papilla differentiation, restricting hair formation especially in secondary and tertiary hairs. This Sox18 mutation also prevented neonatal dermal cells or dermal papilla spheres from inducing hair in regeneration assays. Microarray expression studies identified WNT5A and TNC as potential downstream effectors of SOX18 that are important for epidermal WNT signalling. In conclusion, SOX18 acts as a mesenchymal molecular switch necessary for the formation and function of the dermal papilla in all hair types.

Murine dorsal hair type is genetically determined by polymorphisms in candidate genes that influence BMP and WNT signalling.

Mouse dorsal coat hair types, guard, awl, auchene and zigzag, develop in three consecutive waves. To date, it is unclear if these hair types are determined genetically through expression of specific factors or can change based on their mesenchymal environment. We undertook a novel approach to this question by studying individual hair type in 67 Collaborative Cross (CC) mouse lines and found significant variation in the proportion of each type between strains. Variation in the proportion of zigzag, awl and auchene, but not guard hair, was largely due to germline genetic variation. We utilised this variation to map a quantitative trait locus (QTL) on chromosome 12 that appears to influence a decision point switch controlling the propensity for either second (awl and auchene) or third wave (zigzag) hairs to develop. This locus contains two strong candidates, Sostdc1 and Twist1, each of which carry several ENCODE regulatory variants, specific to the causal allele, that can influence gene expression, are expressed in the developing hair follicle, and have been previously reported to be involved in regulating human and murine hair behaviour, but not hair subtype determination. Both of these genes are likely to play a part in hair type determination via regulation of BMP and/or WNT signalling.

Survival in patients with multiple primary melanomas: Systematic review and meta-analysis.

BACKGROUND: The literature surrounding survival of patients with multiple primary melanomas (MPM) yields variable and opposing findings, constrained by statistical challenges. OBJECTIVES: To critically examine the available literature regarding survival of patients with MPM compared with a single primary melanoma and detail statistical methods used. METHODS: Electronic searches were performed of PubMed, Embase, Web of Science, and Scopus, with cross-checking of references, for the period January 1956 to June 2019. Studies published in English examining survival in patients with multiple melanomas were included. Case studies and small case series were excluded. RESULTS: There were 14 studies eligible for inclusion. Conclusions on survival varied markedly depending on the statistical method used. Four studies that accounted for survival bias by partitioning the survival time were included in the quantitative review, with 3 of these reporting a survival disadvantage for MPM, whereas the fourth showed no difference in survival. The pooled hazard ratio was 1.39 (95% confidence interval, 1.07-1.81) but with significant heterogeneity (I2 = 96.8%, Phet < .001). LIMITATIONS: Studies showed significant heterogeneity in methodology. CONCLUSION: When data were analyzed with robust statistical methods, patients with MPM had a survival disadvantage compared with patients with a single primary melanoma.

Interleukin-23 regulates interleukin-17 expression in wounds, and its inhibition accelerates diabetic wound healing through the alteration of macrophage polarization.

Inflammation is a critical phase in the healing of skin wounds. Excessive inflammation and inflammatory macrophages are known to cause impaired wound closure and outcome. This prompted us to test the role of IL-23 in IL-17 expression and in modulating wound inflammation and macrophage polarization. Full-thickness wounds (4 × 6 mm) were created on the dorsal surface of multiple genetically modified mouse models. Obese diabetic mouse wounds were treated with anti-IL-17A, anti-IL-23, or isotype-matched antibodies. We found IL-23- but not IL-12-deficient mice displayed significantly reduced IL-17 expression in wounds. This was rescued by delivery of recombinant IL-23. IL-23- and IL-17-deficient mice showed a significant increase in noninflammatory macrophages. Obese diabetic mice treated with anti-IL-17A and anti-IL-23p19 blocking antibodies had significantly improved wound reepithelialization. Similarly, IL-17-/- obese mice had accelerated wound closure, resulting in reduced iNOS expression and inflammatory macrophages while maintaining prohealing CD206 and lymphatic vessel endothelial hyaluronic acid receptor 1 (LYVE1)-expressing macrophages. This study highlights the importance of the IL-17 pathway in wound closure offering new possibilities of therapeutic intervention in chronic wounds.-Lee, J., Rodero, M. P., Patel, J., Moi, D., Mazzieri, R., Khosrotehrani, K. Interleukin-23 regulates interleukin-17 expression in wounds, and its inhibition accelerates diabetic wound healing through the alteration of macrophage polarization.

Sun protection behavior after diagnosis of high-risk primary melanoma and risk of a subsequent primary.

BACKGROUND: Melanoma survivors are at high risk of further primary melanomas. OBJECTIVE: To assess sun behavior after melanoma diagnosis and in relation to further primary melanomas. METHODS: We applied repeated measures latent class analysis to reported primary prevention behavior at time of diagnosis and every 6 months for 2 years after diagnosis in patients with clinical stage IB or II melanoma. Correlates of behavior trajectories and risk of subsequent primaries were determined by using multivariable logistic and Cox regression analyses, respectively. RESULTS: Among the 448 male and 341 female patients, sunscreen use fell into 3 trajectories: stable never-use (26% of males and 12% of females), stable sometimes-use (35% of males and 29% of females), and increased to often-use (39% of males and 59% of females). Most reduced their weekend sun exposure, but in 82% of males and 69% of females it remained increased. Males, smokers, the less educated, those who tanned, and those not self-checking their skin were more likely to have trajectories of inadequate protection. Patients with a history of melanoma before the study doubled their risk of another primary melanoma in the next 2 years if sunscreen use in that time was inadequate (hazard ratio, 2.45; 95% confidence interval, 1.00-6.06). LIMITATIONS: Patient-reported data are susceptible to recall bias. CONCLUSION: Our results may assist clinicians in identifying patients not using adequate sun protection and providing information for patient counseling.