Minichromosome maintenance protein 6, a proliferation marker superior to Ki-67 and independent predictor of survival in patients with mantle cell lymphoma.

Minichromosome maintenance protein 6 (MCM6) is one of six proteins of the MCM family which are involved in the initiation of DNA replication and thus represent a marker of proliferating cells. Since the level of cell proliferation is the most valuable predictor of survival in mantle cell lymphoma (MCL), we investigated lymph node biopsy specimens from 70 patients immunohistochemically with a monoclonal antibody against MCM6. The percentage of MCM6 expressing lymphoma cells ranged from 12.0 to 95.6%, with a mean of 61.0%, and was significantly higher than the percentage of Ki-67-positive cells (P<0.0001). Surprisingly, the ratio of MCM6-positive cells to Ki-67-positive cells was higher than in normal stimulated peripheral blood mononuclear cells, indicating a cell early G1-phase arrest in MCL. A high MCM6 expression level of more than 75% positive cells was associated with a significantly shorter overall survival time (16 months) compared to MCL with a low MCM6 expression level of less than 25% (no median reached, P<0.0001). Multivariate analysis revealed MCM6 to be an independent predictor of survival that is superior to the international prognostic factor and the Ki-67 index. Therefore, aside from gene expression profiling, immunohistochemical detection of MCM6 seems to be the most promising marker for predicting the outcome in MCL.

Topoisomerase IIalpha expression in mantle cell lymphoma: a marker of cell proliferation and a prognostic factor for clinical outcome.

Mantle cell lymphoma (MCL) is a malignant lymphoma associated with a relatively aggressive clinical course and a median overall survival time of 3-4 years. Treatment usually consists of combination chemotherapy, often including topoisomerase (topo) inhibitors such as doxorubicin, etoposide and mitoxantrone. Topo IIalpha is an enzyme that is needed whenever uncoiling of DNA is necessary during the cell cycle. The enzyme is a marker of cell proliferation. We analyzed the expression of topo IIalpha in relation to Ki-67 and the clinical outcome in patients with MCL. Biopsy specimens from 95 untreated patients enrolled in two multicenter trials (1975-1985) were investigated immunohistochemically with monoclonal antibodies against topo IIalpha (Ki-S4) and Ki-67 (Ki-S5). Patients with low (0-10%) topo IIalpha expression had a median overall survival time of 49.0 months, compared to 17.0 months for patients with high (more than 10%) topo IIalpha expression. The Kaplan-Meier analysis showed a significant difference in the overall survival time related to the percentage of topo IIalpha (P<0.001) and Ki-67 (P<0.001) positive tumor cells. Multivariate Cox regression analysis revealed the expression of topo IIalpha as the most important prognostic factor (P<0.001) in MCL superior to the international prognostic index (IPI), the Ki-67 index and other clinical characteristics.