Diagnostic aspects of skin cancer and lichen sclerosus studied with laser scanning microscopy

Abstract

Histopathologic examination of tissue biopsies is the current gold standard for the diagnosis of dermatological problems. Similarly, in oncology, sentinel lymph node (SLN) biopsy is the state-of-the-art diagnostic method for me- tastasis screening. Although these methods are safe, they are associated with some limitations, particularly because they are invasive, labor-intensive, and time-consuming. Moreover, histopathological analysis does not always lead to conclusive results. Therefore, there is a need for the development of fast, accurate, and non-invasive diagnostic procedures, complementary to these standard techniques. It seems that laser scanning optical microscopy moda- lities have the potential to meet this need. Regarding this, the present study was conducted to explore the efficiency of two of these methods, namely re- flectance confocal microscopy (RCM) and multiphoton microscopy (MPM), in dermatological and oncological applications. Particular focus was given to lichen sclerosus (LS), basal cell carcinoma (BCC), and malignant melanoma (MM) metastases, all of which are important disorders requiring improved diagnostic methods. This thesis builds upon the work reported in five papers. The first two papers involved the investigation of LS. In the first paper, we reported the clinical signs of LS, namely hypopigmentation, petechiae, and preputial constriction, based on which the diagnosis of LS was established. In the se- cond paper, it was found that RCM could visualize the thick fiber structures corresponding to sclerosis in the dermis, thereby facilitating the differentia- tion of LS from normal penile skin. In the third paper, it was observed that the application of methyl-aminolaevulinic acid (MAL) on BCCs could not increa- se the contrast when imaged with ex vivo MPM. Furthermore, it was found that MAL-induced fluorescence cannot be excited by the expected two-pho- ton excitation route when studied with MPM; rather, a one-photon process (i.e., anti-Stokes fluorescence) takes place. This finding is important not only for diagnostic aspects but also for future work in which photodynamic effects might be required. The fourth and fifth papers involved the investigation of MM metastases in lymph node tissues. It was found that particularly ex vivo

MPM can enable the visualization of the characteristic morphologic features in this type of tissue. Furthermore, by extending the spectroscopic informa- tion to include also fluorescence life-time, the latter has the potential to in- crease the diagnostic ability. Taken together, the obtained results were indicative of the potential of laser scanning microscopy techniques as diagnostic tools for the detection of LS, BCCs, and MM metastases to lymph nodes. Future studies are encouraged to fully explore the potential of these techniques to be used for dermatological and oncological investigations in a non-invasive/intravital manner.