Detection of COL1A1-PDGFB fusion transcripts in dermatofibrosarcoma protuberans

ARTICLE

Auteur(s) : Gen Nakanishi¹, Masae Shirai¹, Takeshi Kato¹, Norikazu Fujii¹, Noriki Fujimoto¹, Toshihiro Tanaka¹, Yoshinori Shirafuji², Norihiro Suzuki², Masaki Otsuka², Kenji Asagoe², Keiji Iwatsuki², Ryo Tanaka³, Wataru Fujimoto³, Fumie Hanawa⁴, Shinji Shimada⁴, Yujin Nakagawa⁵, Miki Tanioka⁵

¹Department of Dermatology, Shiga University of Medical Science, Seta, Tsukinowa-Cho, Otsu, Shiga, 520-2192, Japan
²Department of Dermatology, Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Science, Okayama, Japan
³Department of Dermatology, Kawasaki Medical School, Okayama, Japan
⁴Department of Dermatology, Faculty of Medicine, University of Yamanashi, Yamanashi, Japan
⁵Department of Dermatology, Fukui Red CrossHospital, Fukui, Japan

Dermatofibrosarcoma protuberans (DFSP) is a mesenchymal neoplasm of both dermal and subcutaneous tissues commonly occurring on the trunks of middle aged adults. DFSP is characterized as a low grade sarcoma because it has the potential to be locally aggressive. After excision, recurrence is common and metastasis is not uncommon either.

The COL1A1-PDGFB fusion protein produced by reciprocal translocation, t(17;22)(q22; q13), is the functional key molecule for DFSP. Various reports of DFSP with the COL1A1-PDGFB fusion gene transcripts have been published in the last ten years [1-6], but the true frequency of the abnormality of this fusion gene is unknown. In this study, we examine the COL1A1-PDGFB gene fusion transcripts by using the reverse transcriptase polymerase chain reaction (RT-PCR) in DFSP frozen samples of 13 Japanese cases in order to define the incidence of this fusion gene expression.

Diagnosis of DFSP was confirmed by histopathological examination and specific staining with anti CD34 antibody before conduction of the gene mutation analysis. After informed consent was obtained from all participants, total RNA was extracted from the frozen tissue sections and reverse transcription was performed. To detect the expression of the COL1A1-PDGFB gene, polymerase chain reaction (PCR) was carried out, using 16 COL1A1 forward primers and a specific PDGFB reverse primer [3]. The PCR product was directly sequenced using an ABI373A automated DNA sequencer.

Table 1 includes the summary of the clinical features of 13 patients and the results of gene mutation analysis, including 4 cases in our previous study [3, 4]. The histological findings of all the samples showed conventional DFSP without fibrosarcomatous areas. Distant metastasis was not detected in any case. Amplifiable RNA, as determined by successful amplification of the G3PDH gene, was obtained from frozen tissue samples of all the patients. The COL1A1-PDGFB fusion transcripts were detected from 11 (85%) of 13 samples from patients diagnosed as having DFSP.
Table 1 The clinical features and fusion genes

To date, a small number of variant translocations without the chromosomal alterations involving chromosome 17 and 21 have been described. In addition, it has been reported that fusion genes other than the COL1A1 and PDGFB are involved in the case of DFSP. In our study, we did not perform fluorescent in situ hybridization analysis and were not able to confirm chromosomal anomalies other than t(17;22) for the COL1A1-PDGFB- negative DFSP cases.

Histopathological and immunohistochemical analysis of 2 cases of COL1A1-PDGFB-negative DFSP demonstrated CD34-positive spindle cells in the reticular dermis extending into the subcutaneous fat. This, however, did notdemonstrate a significant difference between the COL1A1-PDGFB-negative DFSP and other COL1A1-PDGFB-positive DFSP.

The true frequency of the COL1A1-PDGFB fusion gene in DFSP is still unknown. Takahira et al. studied 57 cases of DFSP and observed 74% COL1A1-PDGFB fusion gene transcripts by using paraffin-embedded tissue [5]. Llombart et al. reported that the COL1A1-PDGFB fusion transcripts were detected from 16 (89%) of 18 frozen DFSP samples [6]. In addition to the difference between frozen samples and paraffin-embedded tissue, different primers for PCR were employed in these studies.

RT-PCR analysis of COL1A1-PDGFB fusion transcripts is a very sensitive and reliable technique for diagnosis of DFSP. A small percentage of cases of DFSP are negative, however, for the COL1A1-PDGFB fusion transcripts. Therefore, negative results should be carefully interpreted.

Acknowledgements

References

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3 Nakanishi G, Lin SN, Asagoe K, et al. A novel fusion gene of collagen type I alpha 1 (exon 31) and platelet-derived growth factor B-chain (exon 2) in dermatofibrosarcoma protuberans. Eur J Dermatol 2007; 17: 217-9.

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