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Induction of plasmacytomas with silicone gel in genetically susceptible strains of mice.

BACKGROUND
Plasmacytomas can be induced in high frequency in susceptible strains of mice by the intraperitoneal introduction of plastics or paraffin oils, including the chemically defined oil pristane (2,6,10,14-tetramethylpentadecane). These materials persist in the peritoneal cavity, where they induce chronic inflammation during the long periods before plasmacytomas develop. Such plasmacytomas appear to arise from B cells carrying chromosomal translocations that affect c-myc transcription.


PURPOSE
Because silicone gels are in widespread medical use and share many of the characteristics of other materials known to be inducers of plasmacytomas, we wished to determine their capacity to induce plasmacytomas in mice.


METHODS
In a series of parallel experiments, corn oil, pristane, silicone oil (dimethylpolysiloxane), or silicone gel from commercially obtained mammary implants was injected intraperitoneally into plasmacytoma-susceptible BALB/cAnPt-A and congenic BALB/cAnPt.DBA/2-Idh1-Pep3 mice, as well as into plasmacytoma-resistant C57BL/6N, C3H/HeJ, DBA/2N, and (BALB/c x DBA/2)F1 mice. Mice were examined at least once every 2 weeks for signs of abdominal tumor or weight loss and screened every 4-6 weeks for peritoneal plasmacytoma cells by peritoneal lavage. Tissues were examined by histologic and immunohistochemical techniques. Metaphase chromosome spreads were made from ascitic plasmacytomas without Colcemid treatment, and metaphase plates were G-banded according to standard techniques. The t(12;15) or t(6;15) translocation chromosomes were identified under the microscope in at least five metaphase plates of high banding quality. Mice were autopsied 125-400 days after the injection of test material. Gas chromatography and mass spectrometry were utilized to determine the composition of the silicone oil and silicone gel used in the injections.


RESULTS
The silicone gels tested induced plasmacytomas in BALB/cAnPt-A and BALB/cAnPt.DBA/2-Idh1-Pep3 mice. Neither corn oil used as a control nor 1000-centistoke or 12,500-centistoke dimethylpolysiloxane induced plasmacytomas in these mice. The plasmacytomas were transplantable in syngeneic hosts. Cytogenetic studies of 41 silicone-induced plasmacytomas showed that 30 had t(12;15) translocations, eight had t(6;15) translocations, and three had no translocations.


CONCLUSIONS
The silicone gels used in mammary implants, which contain a complex mixture of different siloxanes, induced peritoneal plasmacytomas in genetically susceptible mice. Silicone gels provide new chemically defined materials that are effective inducers of plasmacytomas in BALB/cAnPt-A and BALB/cAnPt.DBA/2-Idh1-Pep3 mice. Further studies will be required to determine which of the components of these gels are the active materials.