Skin cancer as seen by electrical impedance

Abstract: This thesis describes the relation between skin cancer and electrical impedance. On the cellular level, electrical impedance measured at clinically relevant frequencies is affected by e.g. membrane structure and orientation, and composition of and relation between the intra- and extracellular environments, thus similar properties used by histopathologists to diagnose skin cancer. The aim is to detect skin cancer using the electrical impedance technique. The overall objective is to develop an alternative to visual skin cancer screening. Impedance was measured with a depth selective impedance spectrometer between 1 kHz and 1 MHz of various benign lesions and skin cancers including e.g. malignant melanoma, squamous and basal cell carcinoma, dysplastic nevi, actinic keratosis, and benign pigmented nevi. The lesions were subsequently excised and diagnosed by histopathology. Various pattern recognition tools were used to analyse the impedance data. First of all it was concluded that impedance of lesions differs from healthy skin, which confirms previous publications. It was also concluded that healthy skin varies within small areas on the body, which is a factor, amongst others, that might lower the signal-to-noise ratio of skin cancer impedance. Extensive measurements with a new version of the impedance spectrometer facilitated separation between skin cancer and benign nevi with clinically relevant accuracy. To improve the signal-to-noise ratio, a novel type of electrode that penetrates the outermost layer of the skin was introduced, and it was found that the accuracy varies with electrode and cancer type. Area under ROC curve was 91% for the separation of nevi and melanoma, and 98% for nevi and basal cell carcinoma. The results strongly suggest that the electrical impedance technique can be used to detect skin cancer, i.e. proof-of-principle has been achieved. However, before the technique can be used as a routine instrument in the clinics, additional studies are required.