Internal Tandem Duplication of Exon 8 of c-kit Is Associated With Longer Total Survival in Canine Cutaneous Mast Cell Tumors

Abstract

Canine cutaneous mast cell tumors (ccMCTs) have a highly variable biological behavior and accurate prognostication is essential for therapeutic intervention. Internal tandem duplications (ITD) of exon 11 are the most commonly detected c-kit mutation in ccMCTs and are associated with poor prognosis and increased cellular proliferation. The prognostic value of detecting mutations in other exons of c-kit has not been systematically examined. In this study, we analyzed the prognostic value of ITD mutations of exon 8 in c-kit of ccMCTs in comparison to ccMCTs with ITD mutations of exon 11 and ccMCTs without mutations of exon 8 or 11. The mutational status, histological grade, KIT expression pattern, Ki67 index, AgNOR (argyrophilic nucleolar organizing region) score, and Ag67 score were determined in 221 ccMCTs, and outcome was available for 101 dogs. ITD mutations of exon 8 were found in 73/221 (33%), of exon 11 in 100/221 (45%), and none of these mutations in 50/221 (22%) of ccMCTs. None of the dogs with mutations of exon 8 died due to suspected ccMCT-related cause, but 23% dogs with ccMCTs with mutations of exon 11 died due to suspected ccMCT-related cause. Prognostic parameters in ccMCTs with exon 11 mutations were commonly associated with a high proliferative activity and poor prognosis, while prognostic markers in ccMCTs with mutations of exon 8 had lower values similar to those observed in ccMCTs without mutations in exons 8 or 11 of c-kit. This study indicates that screening for ITD mutations in exon 8 in ccMCTs may be helpful to identify less aggressive ccMCTs and may be recommended as a supplementary prognostic test.

Prognostic value of immunohistochemical markers in canine cutaneous mast cell tumours: A systematic review and meta‐analysis

“…Immuno‐expression of KIT is commonly used in the prognostic evaluation of canine MCTs, and the meta‐analysis of the five studies 43,45,65‐67 involving this immunomarker support the previous findings. In contrast to studies with Ki‐67, the animals involved in the KIT articles were evaluated in the same way in accordance with the KIT expression patterns proposed by Kiupel et al 45 Moreover, the five studies used the same antibody, although the dilutions differed being 1:100 in four studies, 43,45,65,67 and 1:500 in the fifth 66 . Various investigations have correlated the aberrant location of KIT protein and the presence of mutations in the c‐KIT gene with poor prognosis in canine MCT, 6,17,45,52 and the KIT marker is already widely used in immunohistochemical panels.…”

“…All five of the KIT studies assessed the location of the protein following the staining patterns defined by Kiupel et al 45 using rabbit polyclonal anti‐c‐KIT (CD117) antibody (Dako Agilent, #A4502) at dilutions ranging from 1:100 to 1:500. In four of the studies, 43,45,65,66 the association between KIT1 and KIT2/3 patterns with survival time was significant, but this relationship was not observed in the fifth study 67 . Of the 517 tumours evaluated in these five studies, 379 (73.3%) showed positive immunolabelling and were properly classified as 109 (28.8%) presenting KIT1 pattern, 216 (57%) KIT2 and 54 (14.2%) KIT3 (Table 1).…”

“…In the eventuality, OR values could be obtained for only 15 articles that had met the inclusion criteria. Of these articles, 9 (60%) evaluated the cell proliferation immunomarker Ki‐67, 24,38,39,42,43,61‐64 5 (33.3%) focused on the tyrosine kinase receptor KIT, 42,45,65‐67 and 2 (13.3%) analysed the pro‐apoptotic protein BAX 36,68 . An additional two articles evaluated the immunomarker Ki‐67, with a value for HR provided by one 21 and a final OR value presented in the other, 52 but neither were submitted to meta‐analysis because they did not provide all of the data required.…”

“…Nine of the 15 studies included in the meta‐analysis focused on the biomarker Ki‐67 and surveyed a total of 853 animals and 855 tumours 24,38,39,42,43,61‐64 . In all of these studies, mouse monoclonal anti‐Ki‐67 antibody clone MIB‐1 (Dako Agilent, #M7240) was employed at dilutions ranging from 1:50 to 1:400.…”

“…In contrast to the above, considerable research attention has been focused on two additional immunomarkers of canine MCT, namely the cell proliferation marker Ki‐67 24,30,38‐44 and the cell surface marker tyrosine kinase receptor KIT 23,43‐52 . Since the nuclear protein Ki‐67 is present during all active phases of the cell cycle but is absent in quiescent cells, a reliable proliferation index can be established by counting Ki‐67‐positive neoplastic cells 40,53,54 .…”