Optical Coherence Tomography in the Diagnosis of Keratinocyte Carcinomas
OCT is an attractive imaging modality for the diagnosis of keratinocyte carcinoma (nonmelanoma skin cancer), offering the potential for noninvasive detection of early disease. OCT has been most extensively studied for the diagnosis of basal cell carcinoma (BCC) – the most common form of malignancy in humans. In a study of 142 OCT images presented in the absence of additional clinical information the diagnostic accuracy for dermatologists experienced with OCT imaging was a sensitivity of 86–95% and a specificity of 81–98%.[33] When used in combination with clinical evaluation for the evaluation of nonpigmented lesions suspicious for BCC, the addition of OCT did not significantly improve sensitivity, but specificity increased significantly from 29% by clinical assessment to 54% using dermoscopy and to 75% with the addition of OCT.[34]
Scoring systems have been developed to aid the diagnosis of BCC.[35,36] For example, the Berlin score evaluates the presence of features including a dark border beneath the tumour, hyporeflective nests, ovoid structures and disruption of the dermoepidermal junction.[36] A systematic review, published in the British Journal of Dermatology, included 901 cases of BCC in 31 studies from 2003 to 2015.[37] The overall sensitivity and specificity for BCC diagnosis by OCT were 89·3% and 60·3%, respectively, with Fourier-domain OCT exhibiting the best accuracy: 93·7% sensitivity and 61·4% specificity.
A few studies have evaluated the role of angiographic OCT in the diagnosis of BCC. Characteristic features of angiographic OCT imaging include elongated perpendicular vessels in cross-section and dilated vessels.[38,39] There is preliminary evidence that vascular morphology may correlate with the subtype of BCC.[40] A potential application of OCT is in defining tumour margins for BCC preoperatively. This can reduce the number of stages required for staged tumour excision.[41–44] OCT may also have a role in monitoring for recurrence following treatment of BCC with topical therapies,[45,46] photodynamic therapy[47,48] and laser,[49] all of which are associated with substantially higher recurrence rates than surgical excision. OCT has also been used to evaluate the response of BCCs to systemic hedgehog inhibitors.[50]
Cutaneous squamous cell carcinoma (SCC) is another common form of keratinocyte carcinoma that, unlike BCC, has the potential to metastasize. Early recognition and treatment are paramount in reducing this risk. OCT has been assessed for its use in diagnosing SCC and in distinguishing preinvasive disease – actinic keratosis (AK) and Bowen disease – from invasive SCC.[35,51–53] Morphological features that distinguish SCC from preinvasive disease include thickened or disorganized upper epidermis, disruption of the normal skin layers and abnormalities of the dermoepidermal junction.[45]
Diagnostic algorithms have been proposed to distinguish healthy skin and AK from SCC by OCT.[35,54] The sensitivity and specificity for experienced operators were 93·8% and 98·9%, respectively, for SCC diagnosis and 81·6% and 92·6% for AK diagnosis.[54] However, it is noted that hyperkeratotic AKs, which are thought more likely to progress to SCC, were excluded from the study and therefore this high level of accuracy may not translate to lesions typically encountered in the clinic.
Angiographic OCT has also been evaluated in the differentiation of AK, Bowen disease and invasive SCC. A blinded, randomized analysis of 162 angiographic OCT images identified characteristic features from each subtype.[55] Another study of 52 lesions (including AK, BCC and SCC) supported the hypothesis that these exhibit distinct features of angiographic OCT.[39,55]
The British Journal of Dermatology. 2021;184(6):1014-1022. © 2021 Blackwell Publishing
