Second harmonic generation microscopy as a cancer diagnosis tool

Summary form only given. Optical microscopy is one of the most important tool for understanding biology processes. Recently with the advance of femtosecond laser all the nonlinear optical processes have been included into optical microscopy methods and Second Harmonic Generation (SHG) microscopy has emerged as a powerful new optical imaging tool with applications in disease diagnostics [ 1-2]. The "gold standard" in cancer diagnostics is still the traditional histology analysis where accuracy depends on the experience and interpretation skill of the pathologist. A major development would be to use the SHG microscopy as a quantitative tool to cancer diagnosis. Here we show SHG imaging results of the collagen fibers in prostate cancer tissue that can be directly correlated with the cancer malignancy diagnostic [3]. We performed SHG imaging in a back-scattering geometry on the histological slides from the same biopsies that were analyzed by the pathologist. We studied prostate from patients treated at the the Urology Center of UFMG Hospital, Belo Horizonte. A 1 mm diameter punch biopsy was extracted from multiple peripheral zone of the prostate showing normal tissue and cancer tissue with Gleason scores ranging from 3 to 5. The study was approved by the UFMG Institutional Review Board and the Brazilian National Health Committee on the use of humans as experimental subjects. Written informed consent was obtained from all participants before their biopsy procedures. Figure 1 shows SHG images for normal and cancer tissue. The SHG images show major differences on the collagen fiber alignment that changes with cancer progression. The average direction of the fibers in the image was calculated and we obtained a value for the fiber anisotropy [4]. The statistical analysis is presented in the boxplot in figure 1. Note that both the average values (crosses) and the median lines (black center lines) are well separated for the normal and cancer tissue.In summary we present SHG measurements for prostate tissue that allows to obtain a quantitative analysis of the collagen fiber alignment. Our results suggest that this new method could be useful as a complementary tool on grading prostate cancer. Financial support: the Brazilian funding agencies Fapemig, CNPq, and Capes.