The Two Standards in Skin Cancer Diagnosis: Sensitivity and Specificity
Diagnosis of skin cancer requires a series of tests using specific tools or devices. Most of the time it even requires a biopsy. Skin cancer can be diagnosed both via visual or dermatoscopic inspection and biopsy or surgical inspection, and yield either of two results: positive (suspicious) or negative, which translate to being diseased or healthy and free from whatever condition of interest they are testing for.
Let's think of a skin cancer diagnosis here. The process itself typically starts with a visual inspection followed by a biopsy. But between these two, one is always a confirmatory test which leads to the question: How good is a visual inspection in the diagnosis of skin cancer?
Let’s start off by learning about ‘sensitivity’ and ‘specificity’ - the quantifiers of the diagnostic process of skin cancer. Sensitivity refers to the true positive rate or the proportion of correctly identified positives (diseased patients). Simply put, sensitivity is the percentage of correctly diagnosed true positive (suspicious) patients whose visual exam declares positive of skin cancer, further proven by a biopsy. On the other hand, specificity is the rate by which a patient is diagnosed negative during the visual exam turns out to be healthy or true negative from a biopsy.
Given a presumable data above, there are 15 true positives and 21 true negatives. To calculate the proportions of these two groups as diagnosed by biopsy, we use the formula for sensitivity and specificity. The results were 15/17=0.88 and 21/27=0.78 respectively. In other words, about 88% of patients with a visually suspicious lesion can expect skin cancer (positive result) after biopsy, while 78% of those with normal visual inspection would be free of skin cancer (negative result).
A published research says that the sensitivity and specificity of visual or dermatoscopic inspection ranged from 50 to 80% [Ref.1] and the actual percentage may vary depending upon the skill and education of healthcare providers.
Enter Spectra-Scope, a CE- and TGA-approved skin cancer diagnosis device which boasts of 97.6% sensitivity and 86.2% specificity [Ref.2].
From a clinical perspective, this conservative approach of asking for more scar-inducing biopsy tests to confirm skin cancer is not necessarily a bad thing. The problem, however, starts if the lesions are in sensitive areas like the face or the arm and legs. If the suspicious lesions are on multiple locations, several incisions for biopsy would be necessary. This situation, plus the desperate need to avoid unnecessary scarring, creates the need for healthcare providers to give instant, scar-free but highly accurate (in both sensitivity and specificity) diagnosis of all types of skin cancer. Much like the diagnosis that doctors who use Spectra-Scope can give.
[Ref.1] Journal of clinical oncology, volume 24 number 12 April 20 2006
[Ref.2] Lasers in surgery and medicine 2019 51 supplement 31 (s9-)