  We introduce LYSTO, the Lymphocyte Assessment Hackathon, which was held in
conjunction with the MICCAI 2019 Conference in Shenzen (China). The competition
required participants to automatically assess the number of lymphocytes, in
particular T-cells, in histopathological images of colon, breast, and prostate
cancer stained with CD3 and CD8 immunohistochemistry. Differently from other
challenges setup in medical image analysis, LYSTO participants were solely
given a few hours to address this problem. In this paper, we describe the goal
and the multi-phase organization of the hackathon; we describe the proposed
methods and the on-site results. Additionally, we present post-competition
results where we show how the presented methods perform on an independent set
of lung cancer slides, which was not part of the initial competition, as well
as a comparison on lymphocyte assessment between presented methods and a panel
of pathologists. We show that some of the participants were capable to achieve
pathologist-level performance at lymphocyte assessment. After the hackathon,
LYSTO was left as a lightweight plug-and-play benchmark dataset on
grand-challenge website, together with an automatic evaluation platform. LYSTO
has supported a number of research in lymphocyte assessment in oncology. LYSTO
will be a long-lasting educational challenge for deep learning and digital
pathology, it is available at https://lysto.grand-challenge.org/.
