Wilms' Tumor Gene 1 (WT1) Protein Expression Pattern Is Associated with Adverse Clinical Outcome among Pre-B-Cell Acute Lymphoblastic Leukemia/Lymphoma (ALL) Patients (pts)
A Mansoor, M Akbari, A Akbari, A Surmawala, E Torlakovic, I Mirza. University of Calgary/CLS, Calgary, AB, Canada; Lion's Gate Hospital, Vancouver, BC, Canada; University of Alberta, Edmonton, AB, Canada; University of Saskatchewan, Saskatoon, SK, Canada
Background: Expression of WT1 gene has been demonstrated in several solid and hematological malignancies. WT1 is thought to play a significant role in leukaemogenesis. Using RT-PCR based analysis, WT1 expression is reported to be a poor prognostic factor among adult luekemia pts. Since, WT1 has been identified as a molecular target for cancer immunotherapy, immunohistochemical (IHC) detection of WT1 in clinical samples is warranted. We evaluated WT1 expression by IHC among ALL pts and correlated it with overall survival (OS).
Design: Pts were identified from institutional files and classified as ALL, utilizing morphology & flow cytometry data (WHO 2001). FFPE BM biopsy tissue was used to create tissue microarray (TMA), under a standardized method. IHC staining was performed using WT1 Ab (6F-H2; Dako) after heat-induced antigen retrieval, utilizing automated immunostainer (Ventana, Tucson, AZ). Staining (Cytoplasmic &/or Nuclear) pattern was scored among blast cells on a 4- tier system; without knowledge of clinical outcome. All pts received standardized chemotherapy +/- BMT. Follow-up (FU) data was collected by chart review. Kapplan-Meier survival plots, Log Rank and Cox regression for overall survival (OS), and Spearman's correlation were used for analyses.
Results: 103 pts (3-73 yrs; median 11 yrs; M:F1.4:1) were included. 82% (84/103) were young (<40 yrs). 91 (88%) pts were pre B-ALL and 12 (12%) pts were T-cell ALL. 43/103 (42%) pts were negative and 60/103 (58%) showed positive staining (cytoplasmic only, equal intensity). WT1+ staining pattern included 1+ (10, 17%); 2+ (15, 25%); 3+ (24, 40%) and 4+ (10, 16%). WT1 expression positively correlated with age (< 40 vs. > 40 yr) (r=0.238, p<0.040) and expression of WT1 was a significant predictor of worse OS in age group <40 yrs (p <0.011). Among Pre-B ALL pts; at median FU of 36 M (range 7-90), 16 (18%) (13 WT1+ vs 03 WT1-) pts died (p 0.035). OS was significantly worse for age >40 (p<0.0001), where WT1 expression made no difference.
Conclusions: Our results show that WT1 protein (as detected by IHC) among ALL pts has cytosolic localization and positive expression is associated with poor overall survival among Pre-B-cell ALL, specially among younger pt (<40yrs).
Tuesday, March 23, 2010 9:15 AM
Platform Session: Section B, Tuesday Morning