Reflectance Confocal Microscopy (RCM) in Malignant Melanoma and Non-Melanoma Skin Cancers

1. Introduction

The landscape of melanoma diagnosis continues to evolve as clinicians seek to balance early detection with the prevention of unnecessary surgical interventions. Histopathological examination remains the gold standard for skin cancer diagnosis; however, skin biopsy is not always feasible in patients with numerous melanocytic nevi, lesions in cosmetically sensitive areas, or pediatric populations. The clinical challenge is reflected in the benign-to-malignant excision ratio, which ranges from 5:1 to 30:1, depending on clinician expertise and specialization [1, 2].

Melanoma research increasingly emphasizes early and accurate diagnosis as the most effective approach for optimizing prognosis and the most cost-efficient strategy for disease management [3]. While dermoscopy provides greater diagnostic accuracy compared to naked-eye examination, its clinical utility is limited by the high rates of unnecessary excisions [4, 5, 6].

Recent advances in non-invasive imaging techniques, particularly reflectance confocal microscopy (RCM), offer dermatologists the ability to assess skin lesions immediately without tissue removal [7]. This technology addresses the critical need for improved diagnostic accuracy while reducing healthcare costs and patient morbidity associated with unnecessary procedures.

RCM has emerged as a promising solution, demonstrating particular value in evaluating equivocal lesions with intermediate diagnostic probability (30–70%) [8, 9, 10, 11, 12]. The technology enables non-invasive, real-time assessment of skin lesions and significantly improves diagnostic accuracy and specificity in the assessment of ambiguous cases.

In this chapter, we review its use in the diagnosis and investigation of patients with malignant melanoma, considering its advantages and disadvantages.

2. Reflectance confocal microscopy: Technology overview

RCM is a non-invasive optical imaging technique that enables visualization of skin structures down to the superficial dermis. The system utilizes near-infrared laser light with a wavelength of 830 nm, focusing coherent monochromatic light onto a single point within the tissue. Changes in refractive indices across microscopic structures produce differential backscattering, creating high-resolution images.

The resulting images display highly reflective components—such as melanin and keratin—as bright white elements against a dark background. This strong contrast provided by natural chromophores makes RCM particularly well-suited for assessing pigmented lesions and diagnosing skin cancers.

RCM achieves imaging depths of approximately 200 μm, penetrating to the papillary dermis level. The technique provides cellular-level resolution comparable to histopathology, earning recognition as a” light biopsy.” This capability allows for detailed assessment of skin architecture and cellular morphology without tissue removal, compared to dermoscopy [13]. Table 1 illustrates RCM properties.

The FDA-approved optical imaging modality enables non-invasive, real-time imaging of skin lesions with resolution approaching that of traditional histopathological examination [14]. When integrated with clinical and dermoscopic assessment, RCM significantly improves the accuracy of distinguishing benign from malignant cutaneous neoplasms [15].

Beyond diagnostic accuracy, RCM has shown practical benefits in clinical decision-making. Prospective, real-world studies demonstrate that adjunctive use of RCM can reduce unnecessary resections by more than 30%, lower the benign-to-malignant resection ratio, and reduce the number of resections required [16]. This technique demonstrates high interobserver reproducibility among trained clinicians and confirms consistent interpretation of lesion morphology [17]. RCM is also well-suited for evaluating lesions in cosmetically sensitive or anatomically challenging locations, such as the face, mucosal surfaces, or pediatric patients, where biopsy may be difficult or undesirable [18].

In addition, RCM serves as a valuable adjunct in treatment monitoring, allowing the assessment of lesion clearance following nonsurgical therapies for melanoma in situ or lentigo maligna [19]. Its integration with other diagnostic methods, including dermoscopy, patient risk factors, and clinical judgment, supports a multifaceted approach that increases the accuracy and overall efficiency of melanoma evaluation [16].

3. RCM in melanoma diagnosis

The incidence of melanoma continues to rise, and although it constitutes a minority of cutaneous malignancies, it is responsible for the majority of related mortality rate. Early detection remains essential for improving clinical outcomes; however, the advantages of prompt diagnosis must be balanced against the risks and healthcare costs of unnecessary surgical excisions. When employed alongside clinical and dermoscopic assessments, RCM offers the potential to reduce avoidable procedures while preserving diagnostic accuracy for malignant melanoma [20].

The Pellacani score represents a semi-quantitative algorithm developed specifically for RCM to develop diagnostic accuracy of melanocytic lesions [9]. This scoring system assigns points to specific RCM features associated with melanoma, including: non-edged dermal papillae, atypical cells at the dermo-epidermal junction, sheets of atypical cells in the epidermis, pagetoid infiltration, and basal layer cellular atypia.

Scores range from 0 to 5, with a threshold of ≥3 providing optimal sensitivity (91.9%) and specificity (69.3%). This standardized approach enhances the objectivity in RCM interpretation and has proven effective in reducing unnecessary excisions while maintaining reliable melanoma detection.

Multiple studies have established RCM’s superior diagnostic performance compared to dermoscopy alone in malignant melanoma (Table 2). A comprehensive meta-analysis by Dinnes et al., encompassing 19 study cohorts (2838 lesions, including 658 melanomas), demonstrated that RCM achieved 82% specificity versus 42% for dermoscopy at 90% sensitivity in general suspicious lesions [21]. For equivocal lesions, RCM demonstrated even greater advantages, with specificities of 86 versus 49% for dermoscopy. These improvements translate to clinically meaningful reductions in unnecessary excisions, 280 fewer procedures per 1000 lesions in general suspicious cases, and 296 fewer excisions per 1000 equivocal lesions.

In another meta-analysis study, encompassing 7352 lesions from 32 studies reported sensitivity and specificity of 92% (95% CI: 0.91–0.93) and 70% (95% CI: 0.69–0.71), respectively [22]. Diagnostic sensitivity was consistently high across study designs, although prospective interventional studies demonstrated slightly lower specificity. Accuracy remained robust across all lesion categories, with the highest specificity observed for consecutively enrolled lesions (77, 95% CI: 0.75–0.78) compared with lesions preselected as highly suspicious for melanoma (65, 95% CI: 0.63–0.66). RCM exhibited superior performance relative to dermoscopy, particularly in specificity (56, 95% CI: 0.52–0.60 vs. 38, 95% CI: 0.34–0.42).

In a separate study, the diagnostic utility of intravitreal RCM was assessed in comparison with dermoscopy for the evaluation of melanocytic lesions [12]. A cohort of 203 clinically suspicious moles, 123 melanomas (median Breslow thickness 0.54 mm), and 100 benign control lesions was analyzed, with all imaging performed blinded to histopathology. RCM demonstrated significantly higher specificity for melanoma detection than dermoscopy (68 vs. 32%), while maintaining comparable sensitivity (91 vs. 88%), and exhibited high interobserver agreement in a subset of cases. Misclassification by both modalities occurred in only 2.4% of melanomas, and RCM notably outperformed dermoscopy in light-colored lesions, achieving a specificity of 84% compared to 39%. Importantly, RCM correctly classified all benign control lesions, underscoring its potential clinical value in improving diagnostic accuracy, particularly in challenging lesion subtypes.

In a retrospective analysis of clinically suspicious lesions evaluated with RCM between 2010 and 2017, overall sensitivity and specificity were reported as 98.2 and 99.8%, respectively. These results underscore RCM as a highly accurate, noninvasive, real-time diagnostic modality, capable of assessing skin lesions and potentially avoiding biopsy in the selected cases [7].

A landmark randomized clinical trial conducted across three Italian dermatology centers (2017–2019) enrolled 3165 patients with suspicious skin lesions to evaluate RCM’s impact on clinical decision-making [16]. The study demonstrated that adjunctive RCM results in increasing positive predictive value (PPV) from 18.9 to 33.3%, reducing benign-to-malignant resection ratio from 3.7:1 to 1.8:1, decreasing the number of required resections by 43.4%, and ensuring detection of all clinically significant melanomas (>0.5 mm thickness).

A case study describes a 75-year-old woman with a history of lentigo maligna melanoma who presented with a new brownish-pink papule on the right medial knee [23]. Dermoscopy revealed a biphasic pattern with polymorphic vessels and irregular structures suggestive of melanoma, though irritated intradermal nevus and clonal seborrheic keratosis were also considered. Reflectance confocal microscopy (RCM) demonstrated asymmetry, papillary epidermal features, keratin-filled invaginations, and irregular nests of pleomorphic cells with atypical nuclei at the dermo-epidermal junction, findings consistent with melanoma and lacking features of seborrheic keratosis. Histopathology confirmed a 0.5-mm-thick maculopapular melanoma with junctional and dermal nests of atypical melanocytes, nuclear pleomorphism, and a low mitotic index.

These findings provide robust evidence for RCM’s clinical utility in high-volume referral settings, demonstrating improved diagnostic yield while minimizing unnecessary procedures.

4. RCM in non-melanoma skin cancers (NMSCs)

RCM has emerged as a valuable non-invasive imaging modality in the diagnosis and management of nonmelanoma skin cancers (NMSCs), including basal cell carcinoma (BCC) and squamous cell carcinoma (SCC). RCM provides in vivo, high-resolution imaging of skin lesions, facilitating the assessment of tumor margins, depth, and subtypes, thereby aiding in treatment planning and monitoring.

RCM has demonstrated significant utility in diagnosing basal cell carcinoma (BCC) and delineating tumor margins [24]. A prospective study of 1005 lesions reported that RCM, combined with dermoscopy, achieved sensitivity and specificity values of 93.2 and 51.7%, respectively, for BCC diagnosis [25]. The technique has proven particularly valuable in identifying residual BCC following biopsy, potentially reducing unnecessary surgical procedures [26].

Key RCM features of BCC include, tumor islands with peripheral palisading, increased vascularity in the dermis, polarized nuclei at the periphery of tumor nests, and clefting artifacts around tumor islands.

For BCC lesions unequivocally identified as malignant by RCM, clinicians may proceed directly to definitive surgical excision rather than performing a partial biopsy, thereby achieving the complete treatment in a single procedure [27]. This “one-stop” approach has been shown to be non-inferior in achieving tumor-free margins while substantially enhancing patient satisfaction due to its convenience compared with conventional management. Looking forward, RCM has the potential to streamline both diagnosis and treatment during the initial consultation, potentially obviating the need for a preliminary diagnostic biopsy.

In squamous cell carcinoma (SCC), RCM aids in distinguishing between invasive and in situ lesions while assessing differentiation grades. Studies evaluating SCC cases have identified specific dermoscopic and RCM criteria that can predict invasiveness and differentiation patterns [28]. Additionally, RCM facilitates monitoring of treatment response in SCC in situ following therapies such as photodynamic therapy [29].

Characteristic RCM features of SCC include disorganized epidermal architecture, atypical keratinocytes with enlarged nuclei, loss of normal honeycomb pattern, and increased inflammatory infiltrate.

A review of eight studies including 352 NMSC lesions (seven basal cell carcinomas and one squamous cell carcinoma) assessed the performance of dermoscopy, RCM, and optical coherence tomography (OCT) in detecting residual tumor after nonsurgical treatment [30]. Meta-analysis demonstrated that RCM offered the best combined diagnostic accuracy for basal cell carcinoma clearance, with a sensitivity of 100% and specificity of 72.5%, while OCT achieved 86.4% sensitivity and 100% specificity. In contrast, clinical examination and dermoscopy, though standard tools for monitoring, showed the limited reliability in confirming complete clearance.

5. RCM advantages and disadvantages

RCM provides a non-invasive, real-time imaging procedure that enables near-histological resolution of the skin without the need for biopsy. This technology allows in vivo visualization of the entire epidermis, dermo-epidermal junction, and papillary dermis at the cellular level, which is particularly valuable in areas with specific concerns such as the face or mucosa. By providing precise visualization of tumor architecture, RCM supports more targeted interventions and may improve both clinical outcomes and cosmetic results [6, 31, 32]. The development of hand-held RCM devices has further enhanced its applicability by enabling imaging of curved or difficult-to-access areas [33, 34, 35, 36].

RCM improves diagnostic accuracy for melanoma and non-melanoma skin cancers, especially when combined with dermoscopy. Studies have reported sensitivity up to 95% and specificity around 84% for melanoma detection, with meta-analyses confirming improved diagnostic yield and reduced unnecessary excisions of benign lesions [36, 37]. In basal cell carcinoma, RCM has shown sensitivity of 86–96% and specificity of 89–99% for margin assessment, making it a useful adjunct to Mohs micrographic surgery [35, 36, 37, 38]. Its strong correlation with histopathology allows for more targeted biopsies and facilitates the interpretation of heterogeneous lesion [38].

Beyond diagnosis, RCM contributes to treatment planning and follow-up of skin cancers. Studies have demonstrated its ability to accurately delineate lateral tumor margins in both melanoma and non-melanoma skin cancers, which may contribute to a reduction in the number of surgical layers required for complete excision [39, 40]. This capability is particularly advantageous for lesions with poorly defined borders, such as those on sunburned skin of the exposed area, as well as for hypomelanotic lesions and lesions exhibiting regression structures on dermoscopy, where conventional assessment may be challenging.

Another key advantage of RCM is its role in dynamic monitoring and follow-up of treatment. It has been applied to evaluate responses to non-surgical therapies, including topical agents, photodynamic therapy, and cryotherapy, as well as in longitudinal studies of skin responses to external stimuli such as ultraviolet radiation [38, 41]. By reducing the number of unnecessary biopsies and surgical interventions, RCM not only improves patient care but also generates substantial healthcare savings, with one study reporting annual cost reductions exceeding €280,000 per one million population [42].

Despite its many advantages, several limitations restrict the widespread clinical adoption of RCM. The foremost technical limitation is its restricted depth of penetration, reaching only the upper papillary dermis (~200 μm) [14]. This limitation prevents adequate visualization of deeper dermal structures, making RCM less reliable for detecting nodular or thick melanomas, where subsurface tumor components may be missed [43].

Another major limitation is the steep learning curve associated with image interpretation. Unlike dermoscopy, which has been broadly integrated into routine screening, RCM produces grayscale images that require interpretation based on histomorphological features rather than clinical patterns. Diagnostic accuracy is therefore highly dependent on operator expertise [13, 44]. Farnetani et al. demonstrated that experienced users achieved significantly higher sensitivity in melanoma detection compared to novices (91.0% vs. 84.8%) [17]. The price of RCM device, time-intensive nature of image acquisition and analysis further reduces its feasibility for large-scale or high-volume screening [33].

RCM also exhibits reduced effectiveness in certain lesion types and anatomical sites. Heavily pigmented or highly keratinized lesions, ulcerated tumors, and lesions with dense adnexal structures may generate imaging artifacts that obscure cellular details [45]. Similarly, the en face orientation of RCM images may lead to poor contrast in nonpigmented lesions, complicating the differentiation of superficial basal cell carcinoma and other nonmelanotic skin cancers [46]. Lesions located on mucosal surfaces or acral skin may also pose challenges due to surface curvature, tissue mobility, or patient discomfort during imaging [47].

Interpretation difficulties represent another drawback. Distinguishing between activated Langerhans cells and dendritic melanocytes can be problematic, leading to potential false-positive diagnoses of melanoma in vivo [48]. Although RCM improves specificity, it does not eliminate false-positive findings, particularly in inflammatory or atypical benign lesions, which may still result in unnecessary biopsies and patient anxiety [49].

Finally, the lack of standardized diagnostic criteria and reporting protocols hinders consistent clinical integration and limits comparability across studies [33]. Until these standards are fully established, variability in interpretation and reporting remains a significant challenge for broader adoption.

6. Conclusion

In conclusion, RCM is a valuable, noninvasive, and cost-effective dermatological imaging that increases diagnostic accuracy and serves as an important adjunct tool alongside dermoscopy and histopathology in modern dermatology. However, its practical limitations, including limited availability, the need for specialist expertise, and the potential for interpretive variability, underscore the necessity for appropriate patient selection and comprehensive operator training. Accordingly, RCM is best employed as a complementary diagnostic approach, in combination with the established techniques, to optimize clinical decision-making and patient outcomes.