QS139. A LEPORINE MODEL FOR THE STUDY OF AUTOL- OGOUS AMNIOTIC MESENCHYMAL STEM CELL- BASED THERAPIES. Shaun A. Steigman 1 , Myriam Ar- mant 2 , Azra Ahmed 1 , Dario O. Fauza 1 ; 1Children’s Hospital Boston, Harvard Medical School, Boston, MA; 2CBR Insti- tute for Biomedical Research, Harvard Medical School, Bos- ton, MA Background: The amniotic fluid has been shown to bear a unique population of mesenchymal stem cells (MSCs). Different surgical cell-based therapies utilizing amniotic MSCs have been validated experimentally, in perinatal sheep models. Ovine models, how- ever, are very costly, time consuming, and logistically demanding. Compared to sheep, a rabbit model would be significantly more cost-effective, demand less infra-structure, yield more fetuses per mother, and consume less time. Our aim was to determine the viability of a leporine model for the study of autologous amniotic mesenchymal stem cell-based therapies. Methods: Fourteen time- dated, G1P0 pregnant New Zealand does containing a total of 122 fetuses underwent a laparotomy at 23-24 days gestation (term 32 days). After placing two uterine stay sutures to affix the chorion and the amnion to the myometrium, a 1 cm hysterotomy was performed on the distal-most amniotic cavity of both uterine horns (n=28). The amniotic fluid was procured under direct vision (fig- ure), the ear ipsilateral to the horn was partially resected to mark the fetus, and the gestational membranes, uterus, and abdomen were closed. Normal delivery was allowed. Amniotic MSCs were isolated and expanded in media containing fetal bovine serum (FBS) and basic fibroblast growth factor (bFGF). Multi-color flow cytometry with rabbit-specific antibodies to CD44, CD45, and CD90 was performed on expanding undiffer- entiated cells. Cells were further exposed to standard adipogenic and osteogenic culture conditions; and their phenotype was eval- uated by oil-o-red, alizarin red, and von Kossa stains, as appropriate. Results: All does survived surgery. One large inci- sional hernia was the sole maternal complication and did not interfere with delivery or nursing. Fetal survival to term was 37% (40/122) overall and 32% (9/28) for the operated fetuses. Five mothers aborted all or part of their litters. In three of those five does a sizeable amount of blood had been observed between the myometrium and the gestational membranes on both uterine horns at the time of laparotomy, prior to hysterotomy. All surviv- ing fetuses remained alive until weaned from their mothers, ex- cept one. Amniotic fluid sample volumes ranged from 0.20 to 1.00 mL (mean 0.600.19mL). Cells with a typical mesenchymal mor- phology could be successfully isolated and expanded from 75% (21/28) of the samples within 10 days of procurement. Cell popu- lation doubling times ranged from 1 to 2 days, at 10% FBS and 5ng/mL bFGF. Flow cytometry demonstrated positive expression of CD44 and CD90 and negative expression of CD45, in a pheno- type consistent with that of a mesenchymal progenitor cell. Adi- pogenic and osteogenic differentiation was confirmed by the re- spective stains. Conclusions: Surgical procurement of amniotic fluid and concomitant fetal marking, followed by consistent isola- tion and expansion of amniotic mesenchymal stem cells, is viable and reproducible in a leporine model. Although the fetal loss rate is non-trivial, the cost-, resource-, and time-savings versus the ovine model are noteworthy. This rabbit model can serve as a practical and cost-effective basis for amniotic MSC-based experi- mentation. QS140. MALIGNANT BREAST CANCER IN CHILDREN: A REVIEW OF 75 PATIENTS. Juan C. Gutierrez 1 , Nadine Housri 1 , Leonidas G. Koniaris 1 , Anne C. Fischer 2 , Juan E. Sola 1 ; 1 University of Miami Miller School of Medicine, Mi- ami, FL; 2 UT Southwestern/Children’s Medical Center, Dal- las, TX Objective: To examine the current incidence trends and outcomes for pediatric patients with malignant breast cancer. Methods: The SEER registry was examined for all females from birth to 19 years of age diagnosed with a malignant breast cancer between 1973 and 2004. Results: A total of 75 pediatric patients with malignant breast cancer were identified. The median length of follow-up was 53 months for all patients and 67 months for sur- vivors only. Overall, 14.5% of patients had in situ tumors while 85.5% had invasive disease. Tumors were classified as being ei- ther carcinomas (n = 41, 54.7%) or sarcomas (n = 34, 45.3%). The majority of sarcomatous lesions were Phyllodes tumors (n = 29, 85.5%) while most carcinomas were of a ductal etiology (n = 19, 46.3%). The age-adjusted incidence of all malignant pediatric breast cancer in 2003 was 0.08 cases per 100,000 people. Incidence rates for carcinoma and sarcoma subgroups the same year were 0.03 and 0.06 cases per 100,000 people, respectively. There were no significant trends observed in incidence rates during the study period. In the carcinoma group, regionally advanced disease was present in 11 patients (26.8%) while only 3 patients (7.3%) pre- sented with metastatic disease. All patients with sarcomatous tumors presented with localized disease. The median age at the time of diagnosis was 19 years for the carcinoma group (range 11-19 years) and 16.5 years for the sarcoma group (range 12-19 years). Greater than 67% of patients in both groups were identi- fied as Caucasian. Adjuvant radiation therapy was administered in only 9.8% of carcinomas and 8.8% of sarcomas, while 85.4% of carcinoma patients and 97.1% of sarcoma patients underwent surgical resection for their disease. Disease-specific survival for all patients was 75.2% at five years and 69.6% at ten years. Subgroup analysis revealed both five and ten-year survival rates of 89.6% for patients with sarcomatous tumors. Individuals with carcinoma had five and ten-year survival rates of 63.1% and 54.3%, respectively. Conclusions: Malignant pediatric breast cancer remains a relatively rare disease with stable incidence rates. The two most common histologies of these neoplasms are Phyllodes tumors followed by ductal carcinomas. Sarcomatous lesions, including Phyllodes tumors, are associated with excellent outcomes in the pediatric population, whereas carcinomas dem- onstrate a much worse prognosis. Surgical removal remains the primary modality of treatment for these tumors along with a limited role for radiation therapy. Although rare, malignant dis- ease must always be considered in the differential diagnosis of the pediatric patient with a breast mass. 323 ASSOCIATION FOR ACADEMIC SURGERY AND SOCIETY OF UNIVERSITY SURGEONS—ABSTRACTS