Total Tumour Mass Score (TTM): a New Parameter in Chronic Lymphocytic Leukaemia

S ummary . Total tumour mass score (TTM) is introduced as a new parameter in chronic lymphocytic leukaemia (CLL) in order to assess the tumour mass within all major body compartments. TTM is the sum of: (1) the square root of the number of peripheral blood lymphocytes per nl, (2) the diameter of the largest palpable lymph node in centimetres, and (3) the enlargement of the spleen below left costal margin in centimetres. The validity of the proposed scoring system was evaluated in a prognostic study on 256 CLL patients. Patients with high TTM (>9.0) at presentation had the expected median survival (EMS) of 39 months whereas patients with low TTM (<8.9) had EMS of 101 months ( P < 0.0005). TTM was a significant prognostic factor even when adjustment was performed for age, sex, lymphocyte count, response to therapy, TTM-distribution pattern and bone marrow failure. In contrast, the lymphocyte count was not prognostically significant when adjustment was performed for TTM. This suggests that TTM is a better indicator of tumour cell burden than the lymphocyte count. TTM measurement enables the analysis of the tumour mass size independently of other factors. TTM is a simple, objective parameter that can be measured as a continuous quantitative variable allowing derivation of new factors. TTM-doubling time and TTM-response to therapy were significant for prognosis ( P < 0.0005). The proposed scoring system can also be used for the study of the tumour mass distribution pattern.