The testis. A protected environment for leukaemic cells against cyclophosphamide in a mouse model.

Groups of BDF1 mice, inoculated either IM or by the intratesticular (IT) route with comparable numbers of L1210 cells, died within the same time range from the disseminated disease. Cyclophosphamide (100 mg/kg IP) given on day 6 after inoculation, when the disease was advanced, increased the lifespan by about 100%, but all the mice died. The same dose on day 3 effectively cured all mice inoculated IM, whereas those injected with cells into the testicular lymphatic sinusoidal system died with only a short prolongation of lifespan. The study indicates that L1210 cells present in the testis are relatively protected from the action of cyclophosphamide, and the experimental results are consistent with clinical evidence for the occurrence of relapse in children with ALL due to malignant lymphoblasts persisting in the testicular environment.