[Impact of algorithms proposed by the Cutaneous Lymphoma French Study Group for diagnosis of cutaneous lymphoproliferations].

After a first diagnosis proposition, management of cutaneous lymphomas requires a systematic review by an expert pathologist and each case is presented to a multidisciplinary meeting in the setting of the French Study Group of Cutaneous Lymphomas to propose an adequate treatment. A retrospective study of the 2760 cutaneous lymphoproliferations retrieved between 2010 and 2011 were analyzed and demonstrated the interest of diagnostic algorithms we built with the group. The objective of our study was to compare two cohorts from 2010-2011 and 2015-2017 regarding the proportion of cases sent for validation or expertise, the concordance and mismatch rates and potential diagnostic issues using our diagnostic algorithms. Between 2015-2017, 5640 skin lymphoproliferation cases were examined. It appeared that Pathologists were more confident and effective in finding the right diagnosis. Indeed, the rate of concordant diagnosis increased from 57% to 67%. Moreover, in comparison with the 2010-2011 concordant cases sent for expertise, 73.5% of concordant cases were sent for validation in 2015-2017. 14% of cases remained discordant, mainly sent for expertise. Furthermore, half of questionable cases (26.3%) were resolved after expertise, and 12.1% cases remained unsolved. These priority cases are important to be presented at multidisciplinary meeting. The analysis of discordant and doubtful cases unveiled recurrent diagnostic problems for which we proposed appropriate diagnostic algorithms including large B cell lymphomas, CD4+ T cell lymphoproliferations, epidermotropic CD8+ T-cell lymphoproliferations and the differential diagnosis of mycosis fongoïdes/Sezary syndrome versus inflammatory dermatitis.