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Open Access Research article

Establishment and characterization of pleomorphic adenoma cell systems: an in-vitro demonstration of carcinomas arising secondarily from adenomas in the salivary gland

Satoshi Maruyama12, Jun Cheng1, Susumu Shingaki3, Takashi Tamura4, Shuichi Asakawa5, Shinsei Minoshima6, Yoshiko Shimizu4, Nobuyoshi Shimizu7 and Takashi Saku12*

Author Affiliations

1 Divisions of Oral Pathology, Department of Tissue Regeneration and Reconstruction, Niigata University, Graduate School of Medical and Dental Sciences, 2-5274 Gakkoucho-dori, Chuo-ku, Niigata 951-8514, Japan

2 Oral Pathology Section, Department of Surgical Pathology, Niigata University Hospital, 1-754 Asahimachi-dori, Chuo-ku, Niigata 951-8520, Japan

3 Divisions of Reconstructive Surgery for Oral and Maxillofacial Region, Department of Tissue Regeneration and Reconstruction, Niigata University, Graduate School of Medical and Dental Sciences, 2-5274 Gakkoucho-dori, Chuo-ku, Niigata 951-8514, Japan

4 Department of Medical Genetics, School of Health Sciences, Kyorin University, 476 Miyashita-cho, Hachioji-shi, Tokyo 192-8508, Japan

5 Department of Molecular Biology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan

6 Medical Photobiology Department, Photon Medical Research Center, Hamamatsu University School of Medicine, 1-20-1 Handayama, Hamamatsu 431-3192, Japan

7 Advanced Research Center for Genome Super Power, Keio University, 2 Okubo, Tsukuba, Ibaraki 300-2611, Japan

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BMC Cancer 2009, 9:247  doi:10.1186/1471-2407-9-247

Published: 21 July 2009

Abstract

Background

Among the salivary gland carcinomas, carcinoma in pleomorphic adenoma has been regarded as a representative carcinoma type which arises secondarily in the background of a pre-existent benign pleomorphic adenoma. It is still poorly understood how and which benign pleomorphic adenoma cells transform into its malignant form, carcinoma ex pleomorphic adenoma.

Methods

We have established five cell systems from a benign pleomorphic adenoma of the parotid gland of a 61-year-old woman. They were characterized by immunofluorescence, classical cytogenetics, p53 gene mutational analysis, fluorescence in-situ hybridization, and histopathological and immunohistochemical examinations of their xenografts, to demonstrate their potency of secondary transformation.

Results

We established and characterized five cell systems (designated as SM-AP1 to SM-AP5) from a benign pleomorphic adenoma of the parotid gland. SM-AP1 to SM-AP3 showed polygonal cell shapes while SM-AP4 and SM-AP5 were spindle-shaped. SM-AP1-3 cells were immunopositive for keratin only, indicating their duct-epithelial or squamous cell differentiation, while SM-AP4/5 cells were positive for both keratin and S-100 protein, indicating their myoepithelial cell differentiation. Chromosome analyses showed numeral abnormalities such as 5n ploidies and various kinds of structural abnormalities, such as deletions, translocations, derivatives and isodicentric chromosomes. Among them, der(9)t(9;13)(p13.3;q12.3) was shared by all five of the cell systems. In addition, they all had a common deletion of the last base G of codon 249 (AGG to AG_) of the p53 gene, which resulted in generation of its nonsense gene product. Transplanted cells in nude mice formed subcutaneous tumors, which had histological features of squamous cell carcinoma with apparent keratinizing tendencies. In addition, they had ductal arrangements or plasmacytoid appearances of tumor cells and myxoid or hyaline stromata, indicating some characteristics of pleomorphic adenoma.

Conclusion

This study demonstrates in vitro that certain cell types from pleomorphic adenoma are able to clone and survive over a long term and develop subcutaneous tumors in nude mice. The histological features of squamous cell carcinoma from the transplanted cell systems in nude mice might suggest a secondary onset of malignancy from a pre-existing benign adenoma.