C-kit immunohistochemical expression in soft tissue sarcoma

Soft tissue sarcomas are defined clinically and histologically as a heterogeneous group of malignant neoplasms of mesenchymal origin. They develop in connective tissues other than bone, such as skeletal muscle, fat, tendons, fibrous tissue, smooth muscle and the neurovascular elements that support these components. CD117 is a cytokine receptor expressed on the surface of hematopoietic stem cells as well as other cell types. This receptor binds to stem cell factor (a substance that causes certain types of cells to grow). Altered forms of this receptor may be associated with some types of cancer. It was first described by the German biochemist Axel Ullrich in 1987.The detection of c-kit expression by immunohistochemistry has been utilized to identify cancer patients who can be treated with tyrosine kinase inhibitors. Aim of the study
1.This study evaluated c-kit expression in soft tissue sarcomas and its correlation to clinicopathological parameters (age of patients, site, size, depth, histological type, gender, histological grade, stage and clinical presentation) in Iraqi patients. 2.To estimate c-kit expression in soft tissue sarcomas using a specified automated cellular image analysis system (Digimizer) and to correlate this immunohistochemical expression with different clinicopathological parameters (Age, gender, depth, size, site, histological type ,stage, grade of soft tissue sarcoma and clinical presentation) in Iraqi patients. Materials and methods A retrospective and prospective study involving 52 cases which were diagnosed as soft tissue sarcoma were reviewed and collected. These cases were obtained from archival paraffin embedded blocks selected from January 2009 to March 2011 collected from the pathology departments of the teaching histopathological laboratories, Al-Khadhimiya teaching hospital and specialized surgical hospital at the medical city and from the private histopathological laboratories in Baghdad. These cases were obtained by either excisional or incisional biopsy; all the clinicopathological informations including age, gender, site of the lesions, size, depth, histological subtype and grade were reviewed. Five samples paraffin embedded which comprised a positive control group were obtained from the gastrointestinal center in the medical city. These samples were proved to be GIST. Ethical approval for the use of all specimens was obtained and the histopathological diagnosis was confirmed by review of freshly prepared hematoxylin and eosin-stained slides by certified pathologists and classified according to criteria outlined by the World Health Organization (WHO), also the final diagnosis was confirmed by immunohistochemical panels regarding each type. From each formalin fixed paraffin embedded soft tissue sarcoma, one section was stained immunohistochemically for c-Kit. Slides were examined by light microscope at 40x magnification to analyze the expression of c-kit which appears as brown discoloration of the cytoplasm and cell membrane. C-kit expression was assessed according to Quick score, which depends on summation of the number of positive cells and the intensity of c-kit expression.
In addition assessment of immunohistochemical staining was also performed using a specialized automated cellular image analysis system, Digimizer software, version 3.7.0. By this method each slide is examined and three fields that reflect the best of the overall immunostaining of the entire slide were chosen and captured using a Sony digital camera then the assessment of the immunohistochemical expression of c-kit was done through measuring :- 1.The fractional area (in pixels) of positive objects (DAB positives cells),
2.The average intensity of the brown color of the positive cells 3. The digital labeling index which represents the integration of both the area and the intensity of the positively stained cells Results:
•The mean age of patients involved in the current study was 31.76 years with a male to female ratio of 1:1.08, the head and neck region was the most common affected site (31%), and the most common type of soft tissue sarcoma was rhabdomyosarcoma (26.9%), the majority of soft tissue sarcoma cases range between 5-10 cm in their greater diameter (56%) • The majority of cases present as a painless deeply located mass, of poorly differentiated histological type •Forty-one cases (79%) of soft tissue sarcoma out of fifty-two were positive for c-kit expression, while, the remaining eleven cases were negatively stained with c-kit. •By using a specified automated cellular image analysis system (Digimizer) this study reveals a significant difference in the intensity of c-kit expression between the different histological types of soft tissue sarcoma. •There was no significant correlation (p value>0.05) between c-kit expression and the different clinicopathological parameters (age, gender, size, site, depth, clinical presentation, grading and staging of soft tissue sarcoma) revealed through both the manual and the automated methods Conclusion:
1- C-kit was expressed in 79% of soft tissue sarcoma cases 2- There was no significant correlation between c-kit expression and the different clinicopathological parameters (age, gender, size, site, depth, clinical presentation, grade and stage of soft tissue sarcoma) both by the manual and the automated methods.
3- The distribution of cases according to 10 years age intervals revealed 2 peaks, (23%) between 10 to 19 years of age and (21%) between 20 to 29 years with a slight female predominance. 4. The majority of soft tissue sarcoma cases were located in the head and neck region; the rhabdomyosarcoma pattern was the commonest histological pattern. 5- The majority of soft tissue sarcoma cases were of poorly- differentiated type, with stage II disease. 6- The intensity of c-kit expression differs among the variable types of soft tissue sarcoma 7- The use of semiautomated computerized analysis of immunohistochemical marker expression yields more statistically accepted results due to reduced subjectivity and the error, if present, will be systematic.