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Animal models

The Weizmann-Brazil Tumor Bank allows scientists to establish models in which tumors, freshly obtained from patients in the operating room after biopsy or tumor resection, are implanted directly under the skin of genetically engineered animal models in a procedure known as patient-derived xenografts (PDX).

These tumors, which resemble to the greatest possible extent the original tumor growing within the human patient, can then be transferred from the first animal model to additional specimens, eventually propagating the tumors into a large colony - all bearing the same human tumor. This colony provides the researchers with a unique opportunity to perform a large variety of experimental manipulations, in parallel on identical replicas of the original tumor. These manipulations enable the identification of critical genes whose targeting can stop tumor growth or even kill the tumor.

The work of Prof. Yardena Samuels, head of the Weizmann-Brazil Tumor Bank, has already yielded four new PDX mouse strains, and it is hoped that this synergy between the two facilities will generate more use of PDX mice for basic cancer research.

Picture (left): Preparation of a tumor sample extracted from a PDX mouse, prior to implantation into additional animal models.

Examining real cancer samples

The Weizmann-Brazil Tumor Bank receives tissues from biopsied tumors or tumors removed from patients through the cooperation of various medical centers. The images below are examples of human melanoma tissue samples received from Hadassah Medical Center in Jerusalem.

Generally, the samples received are divided into small pieces; some are implanted into immunodeficient mice, and the rest are stored for future use.

Most of the stored samples are kept in the “biobank”, i.e., a -80°C freezer, while a small amount is preserved in formaldehyde, and then processed into paraffin blocks. The scientists cut the blocks into thin slices (6 μm) in order to allow histologic examination of tissue morphology, genes, vessels, etc. 

The sample shown above is from a metastatic melanoma tumor, also known as stage IV melanoma (when cancer cells have spread to other organs). It portrays the tumor cells variability in size, shape, and staining (pleomorphism), as well as the presence of melanocytes (scale bar indicated).