#3033 Background 
 Case-control studies have reported inconsistent results concerning breast cancer risk and polymorphisms in genes that control endogenous estrogen biosynthesis. We report findings from the first study in Mexican women examining associations between female with breast cancer and polymorphisms CYP19 (TTTA repeated polymorphism).
 Methods 
 We conducted a study among 180 healthy women and 70 women with breast cancer underwent hormone therapy with aromatase inhibitor. DNA and questionnaire data was obtained. Tandem repeated (TTTA)n polymorphism in CYP19 gene was determined by PCR followed by electrophoresis on denaturalizing acrilamide gel stained with silver nitrate. Differences were visualized with Gel-Doc BioRad. Estrone, estradiol and FSH levels were measured by RIA and IRMA. We used likelihood-based statistical methods to examine allelic associations.
 Results:
 250 women (age 55 ± 12 years) were included. BMI was 30 ± 7.1 Kg/m2. We found a distribution of different CYP19 allele frequencies. In healthy women the allele frequencies with 6 (32.7 %) and 7 (21.6 %) tandem repetitions were the most frequent, in women with breast cancer the alleles with 6(29%) and 10(26%) tandem repeated were the most frequent. A relationship between hormonal levels and number of (TTTA) repeated was not found. Anastrozol reduced significantly estrona and estradiol. Surpriseling we found in a patients with 10 or more (TTTA)n repeated an association with a mayor tumoral activity (p=0.04).
 Conclusion 
 This study indicates that status of CYP19 >10 TTTA repeated might be related to increased breast cancer risk and with the clinical response (aromatase inhibitor). Because of this is the first study to report an association between CYP19 >10 TTTA repeated and treatment hormonal response in breast cancer. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 3033.

4358 Background Hematopoietic reconstitution after stem cell transplantation requires excessive replicative activity because of the limited number of stem cells that are used for transplantation. Telomere shortening has been detected in hematopoietic cells after allogenic peripheral blood stem cell transplantation (PBSCT). Recent studies have demonstrated shortening of telomeres after chemotherapy, this shortening being equivalent to 15-40 years of ageing which has been related to genetic instability, increase risk of mutations, myelodysplastic syndromes, secondary malignancies and relapse. Aims To measure in vivo the effect of G-CSF administration, on the regulation of stem cells obtained from peripheral blood collected for autologous transplantation and to know its possible implications, on telomere dynamics following high-dose (HD) chemotherapy courses cyclophosphamide (CY) and HD-Ara-C for relapsed non Hodgkin's lymphoma. Methods Telomeric measurement was performed with real-time polymerase chain reaction (RT-PCR),in peripheral blood progenitor cells(PBPC) collected on day 5 and 10 of G-CSF administration from patients with Lymphoma, and day 0,+7,+14 and +17 post transplantation. For CD34+ cells selection, mononuclear cells were isolated from peripheral blood stem cell by Ficoll-Hypaque. The purity of CD34 selected cells was determined in a cell sorter (Becton Dickinson) using a fluorescein isothiocyanate (FICT)-conjugate monoclonal antibody (mAb). Results We have shown dynamic telomere length change during the immediate reconstitution, Telomere Lenght (TL) was shorter in PBPC collected after HD-Ara-C and CY compared to TL after G-CSF administration, 6526bp vs. 4582 bp (P < 0.01). This result was confirmed on CD34+ cells. Engraftment of granulocytes and platelets come on day +13 and +19 respectively An increase in telomere length to day +19 (5962 bp) was found. Unfortunately we face with an early relapse of the same non Hodgkin's lymphoma at day +60. Conclusions Administration of G-CSF increased TL in CD34+ prevents telomere attrition after allogenic peripheral blood stem cell transplantation. The size and composition of the transplanted stem cell pool determines the ultimate telomere length. Whether PBSCT with shortened telomeres has engraftment improvement with G-CSF but risking early relapse warrants more prospective studies. We suggest that measurement of telomere length in peripheral blood collected for transplantation could be useful as a prognostic marker for engraftment/relapse in non Hodgkin's lymphoma without stem cell cryopreservation. Disclosures: No relevant conflicts of interest to declare.