PRAME and Historical Immunohistochemical Antibodies Ki-67, P16, and HMB-45 in Ambiguous Melanocytic Tumors.

ABSTRACT: Ambiguous melanocytic lesions/tumors (AMLs) can be simply described as melanocytic neoplasms that cannot be differentiated as either a melanoma or a nevus. Preferentially expressed antigen in melanoma (PRAME) is a novel antibody that can help differentiate between nevi and melanomas. However, its usefulness remains controversial in AMLs. The aim of this study was to demonstrate the importance of PRAME and diagnostic auxiliary antibodies (Ki-67, p16, HMB-45) in the diagnosis of melanocytic lesions, especially in AMLs. This study included 52 ambiguous melanocytic lesions, 40 nevi, and 40 melanomas. All immunohistochemical studies were performed automatically using the Universal Alkaline Phosphatase Red Detection Kit. Different analytic approaches were used for each antibody based on the literature. Statistically, the multinomial forward stepwise elimination logistic regression analysis was used to create a statistical model to predict the diagnosis of melanocytic lesions based on clinical, morphological, and immunohistochemical data. PRAME positivity was very strong and diffuse in the melanoma group and statistically significantly higher than that of the AML and nevus groups. There was no statistically significant difference between the nevus and AML groups. The Ki-67 proliferation index and HMB-45 staining pattern provided valuable indications for distinguishing between these 3 groups. The P16 antibody was limited in supporting the differential diagnosis. Our statistical model showed that a high mitosis count, central pagetoid spread, and PRAME positivity increased the probability of melanoma against an AML diagnosis. This study showed the advantages of evaluating the PRAME antibody together with morphological features and other immunohistochemical markers (Ki-67 and HMB-45) in the differential diagnosis of melanocytic lesions.

The Comparative Dermal Stimulation Potential of Constant-Volume and Constant-Amount Diluted Calcium Hydroxylapatite Injections Versus the Concentrated Form.

INTRODUCTION: Biostimulation properties of diluted and hyperdiluted calcium hydroxylapatite (CaHA) injections have become increasingly popular. However, the existing data are insufficient to certify a particular dose-response pattern. OBJECTIVE: To assess and compare the dermal stimulation potentials of different concentrations of CaHA injections. MATERIALS AND METHODS: Two independent experiments (Experiment-1: constant injection volume vs Experiment-2: constant CaHA amount) included 4 study groups each, and these experimental groups were placed consecutively on the abdominal skin of a juvenile Yorkshire pig. Histopathological and immunohistochemical stainings were performed on punch biopsy materials collected 4 months after the injection day. RESULTS: The fibroblast count significantly decreased upon dilution from 1:3 to 1:19 in experiment 1 ( p = .000) but still higher than the control group. In experiment 1, the collagen density of the concentrated form was more elevated than the 1:19 dilution and the negative control groups ( p = .034 and .000, respectively) but similar to the 1:3 dilution ( p = .123). No significant difference was observed between the groups regarding collagen density with a standard amount of CaHA (0.2 mL, 30%) ( p > .05). CONCLUSION: Despite the efficacy being more pronounced till 1:3 dilution, hyperdiluted CaHA at any dilution ratio up to 1:19 can provide a higher fibroblast count than the negative control group.

Dermatoscopic and Dermatopathologic Features of a 3-Year-Old Buried Polypropylene Suture.

ABSTRACT: Cutaneous foreign bodies are a well-known cause of delayed wound healing and complications such as abscesses, fistula formation, and secondary infections. Polypropylene sutures are widely utilized in cutaneous surgery because they easily travel through tissues while eliciting minimal tissue reactions. Despite these advantages, retained polypropylene sutures can cause complications. The authors report a case of a retained polypropylene suture that remained buried after a total excision 3 years prior. It started to cause cutaneous symptoms when the patient began exercising 1 week prior to presentation. The authors also examine the dermatoscopic and dermatopathologic features and other complications related to retained polypropylene sutures that have been reported in the literature.

Melanocytes as the source of the increased melanisation in pigmented epithelial tumours: a holistic approach.

BACKGROUND: We aimed to elucidate the causes of the increased melanisation in basal cell carcinoma (BCC) and seborrheic keratosis (SK), and the role of melanocytes in this process. METHODS: This study was a retrospective-cohort study conducted in the pathology department of a university hospital between January 2019 and October 2020. Forty-nine SK and 30 pigmented BCC were included in our study. SRY-box transcription factor 10 (SOX10), CD68, and Masson-Fontana staining was used for analysis in all samples. A representative section of each specimen was photographed under ×400 magnification to facilitate the assessments of the morphology of the melanocytes and their following morphometric parameters: density, nuclear diameter, and distribution. The density of pigmented keratinocytes in the lesional epidermis was scored. The nuclear diameters of melanocytes located in the nonlesional epidermis, the density of the melanophages, and the presence or absence of ulceration and solar elastosis were also recorded. RESULTS: The morphometric findings confirmed a statistically significant increase in melanocyte density in the BCC group compared with that in the SK group (p < 0.001). Moreover, the nuclear minor diameters in the melanocytes of the BCC sections were significantly higher than those in the SK specimens (p < 0.001). The epidermal melanocytes were distributed diffusely in almost all BCC specimens (96.7%), whereas they were mainly limited to the basal layer in the majority of the SK sections (59.2%). The number of epidermal melanised keratinocytes with a score of 3 was significantly higher in the SK group (n = 31; 63.2%) than in the BCC group (n = 6; 20%) (p = 0.001), and they were the main cells representing the pigmented appearance of the tumours. No significant difference was found between both tumour groups in terms of their melanophage density scores (p = 0.206). DISCUSSION: This study is the first step towards an objective quantification of the melanocytes in pigmented epithelial tumours and may provide a morphological background for future studies on these skin lesions.

CD123 immunoexpression in cutaneous lupus erythematosus, polymorphous light eruption, pityriasis rosea, and mycosis fungoides.

INTRODUCTION: CD123-positive plasmacytoid dendrocytes are prominent in the infiltrate of cutaneous lupus erythematous. AIM: To determine the significance of the CD123 immunostain, which labels plasmacytoid dendritic cells (PDC), in cutaneous lupus erythematous (CLE), polymorphous light eruption (PLE), pityriasis rosea (PR) and mycosis fungoides (MF). MATERIAL AND METHODS: A total of 76 cases, including MF (n = 27), CLE (n = 19), PR (n = 19), and PLE (n = 11), were included in the study after reviewing their diagnostic clinical features and pathologic findings. The primary antibody against CD123 was performed in all cases. RESULTS: CD123+ immunostaining in PDCs was positive in all cases. The highest mean percentage was noted in CLE (15.2%), followed by PLE (15%), PR (8.8%), and MF (2%). Besides, the clustering of CD123-positive cells was significant in CLE and PLE compared to MF and PR. CONCLUSIONS: PDC may have an important role in the aetiology of PLE and CLE cases. CD123 is a useful marker for differentiating CLE and PLE from MF and PR.

KRAS, BRAF, PIK3CA mutation frequency of radical prostatectomy samples and review of the literature.

OBJECTIVE: The molecular basis of prostate cancer is highly heterogeneous. Our study aimed to perform the mutation analysis of KRAS, BRAF, PIK3CA, and immunohistochemical (IHC) evaluation of EGFR, HER2, p16, and PTEN to demonstrate new areas for targeted therapies. METHODS: A total of 24 prostatectomy samples diagnosed with adenocarcinoma were analyzed by microarray hybridization. Also, these samples were IHC stained for EGFR, HER2, P16, and PTEN. The cases were divided into two groups based on low and high Gleason scores. All findings were compared with the clinicopathological parameters of the patients. RESULTS: While KRAS mutation was in 3/24 (12.5%) of our cases, BRAF and PIK3CA mutations were not detected. There was no significant difference between the groups in terms of KRAS mutation frequency. HER2 was immunohistochemically negative in all samples. There was no correlation between EGFR, P16 immunopositivity, and clinicopathological features. CONCLUSION: KRAS mutation frequency is similar to those in Asian populations. BRAF and PIK3CA mutation frequencies have been reported in the literature in the range of 0-15% and 0-10.4%, respectively, consistent with our study findings. HER2 immunoexpression is a controversial issue in the literature. EGFR and p16 expressions may not correlate with the stage.

Chondroprotective effect of Nigella sativa oil in the early stages of osteoarthritis: an experimental study in rabbits.

PURPOSE: Nigella sativa oil possesses a well-known ability to protect certain organs from oxidative, neoplastic, and inflammatory damage. This study investigated the potential chondroprotective effects of intraarticular injections of Nigella sativa oil in a rabbit osteoarthritis model. METHODS: Osteoarthritis models were created by performing anterior cruciate ligament transections in 20 New Zealand rabbits. Rabbits were randomly divided into two groups of 10 and given intraarticular injections in their right knees weekly for 5 weeks, beginning in the third week post-operation. Injections given to the first group contained whole Nigella sativa oil, whereas the second group was injected with a saline solution. Knee joints were harvested 8 weeks after surgery. Knee joint surfaces were examined macroscopically, and medial femoral condyle sections were examined microscopically. RESULTS: There was a statistically significant difference in the macroscopic grading results of the groups, with the Nigella sativa group having better results (p=0.001). The Nigella sativa group also received significantly better total Osteoarthritis Research Society International (OARSI) scores (p=0.035). CONCLUSIONS: Intraarticular administration of Nigella sativa oil has the potential to protect cartilage from degeneration in the early stages of osteoarthritis.

Mutation analysis of metastatic melanomas in the central nervous system: results of a panel of 5 genes in 48 cases.

Melanocytic lesions in the central nervous system (CNS) may be primary to the site but are more commonly metastases from cutaneous primaries. In fact, melanomas are one of the most common malignancies that can metastasize to the brain, and some patients may not have a diagnosis of melanoma prior to the discovery of the CNS lesion. In such cases, identifying the primary site may be challenging. We reviewed the archives of a large referral center for melanocytic tumors involving the CNS and selected 48 patients for this study based on our inclusion criteria. We used sequencing to identify mutation status of these tumors and compared these with clinicopathological features. Mutations in exon 9, 11, 13, 17, and 18 of KIT gene, exon 15 of BRAF gene, exon 2 and 3 of NRAS gene, exon 4 and 5 of GNAQ and GNA11 genes were analyzed. Mutations in BRAF-exon 15 were the most common among tumors (58.3%). NRAS-exon 2 and NRAS-exon 3 mutations were detected in 3 and 7 cases, respectively. GNAQ-exon 4, GNAQ-exon 5 and GNA11-exon 5 mutation were present in 1 tumor each. Eight tumors were wild type for all 5 genes, and 6 of these were not known primary despite a work-up and clinical follow-up. Only 1 of these tumors showed a mutation in exon 11 of KIT gene. When compared to primary melanocytic lesions of the CNS, metastatic melanomas were characterized by BRAF gene mutations and wild-type GNAQ and GNA11 genes.

An unusual infiltrative basal cell carcinoma with osteoclastic stromal changes mimicking carcinosarcoma: a case report.

A 91-year-old man presented with an ulcerated nodule on his left lower eyelid. The tumor showed an epithelial component composed of basaloid and clear cells and a stroma that contained many osteoclastic giant cells. Strong, diffuse expression for cytokeratin 17 and p63 was noted in the epithelial component, whereas no staining was present in the sarcomatoid stroma, suggesting that the osteoclast-rich stromal component represented an unusual benign stromal reaction to the carcinoma rather than a manifestation of carcinosarcoma. Further supporting this interpretation was the absence of mitotic figures and low Ki-67 proliferation index (of approximately 1%) in the stromal cells. We herein reported a case of unusual infiltrative basal cell carcinoma, accompanied by a clear cell carcinomatous features and concurrent benign osteoclastic stromal changes.

Minor salivary gland neoplasms.

OBJECTIVE: This study aimed to investigate the clinical presentation, histopathologic and epidemiological aspects, as well as the treatment modalities and outcomes of patients with minor salivary gland tumors (MSGTs). SUBJECTS AND METHODS: A series of 23 patients with MSGTs were reviewed retrospectively. RESULTS: This study included 11 (48%) benign and 12 (52%) malignant tumors of minor salivary glands. Minor salivary gland tumors were more common in men (70%) than in women (30%). The mean age was 31.3 years for benign tumors and 46.3 years for malignant tumors. Pleomorphic adenoma was the most common benign tumor, followed by myoepithelioma. Mucoepidermoid carcinoma and adenoid cystic carcinoma were the most common malignant tumors. The most common symptom was a painless mass of the palate. Surgical treatment was performed in all patients. Adjuvant radiotherapy was used in 3 malignant tumors. Twenty-three patients were followed-up for a median of 5 years. Two patients with malignant tumors underwent a second surgery for postoperative local recurrence. They were successfully treated with the second surgery. CONCLUSIONS: Minor salivary gland tumors are relatively uncommon neoplasms of the head and neck region. There is limited literature on MSGTs. This study provides a versatile approach for MSGTs from demographic data and clinical presentations to treatment modalities and treatment outcomes.

Taurine attenuates lung ischemia-reperfusion injury after lung transplantation in rats.

PURPOSE: Taurine, the major intracellular free amino acid found in high concentrations in mammalian cells, is known to be an endogenous antioxidant and a membrane-stabilizing agent. It was hypothesized that taurine may be effective in reducing ischemia-reperfusion injury after lung transplantation and an experimental study was conducted in a rat model. METHODS: The number of Sprague-Dawley rats used in the study was 35. Animals were randomized into five groups of 7 rats each, including control, donor I, donor II, ischemia-reperfusion injury, and treatment groups. All animals were exposed to the same experimental conditions in the preoperative period. Rats were fixed in a supine position after the induction. After the rats were shaved, a left pneumonectomy was performed following sternotomy in control, donor I, and donor II groups. The harvested grafts in donor I and donor II groups were transplanted to the rats of the ischemia-reperfusion group and treatment group, respectively. However, taurine was administered intraperitoneally for 3 days before the harvesting procedure in donor II. All harvested lungs were kept in a Euro-Collins solution at +4 °C for 24 h in a half-inflated manner. After harvesting and transplantation, lungs were sampled for histopathological and biochemical analysis. RESULTS: Malondialdehyde and superoxide dismutase, glutathione peroxidase, and catalase levels were lower in the treatment group than the other groups (p < 0.05). Histopathological findings were better in treatment group than the ischemia-reperfusion group (p < 0.05). CONCLUSION: It was demonstrated that donor treatment with taurine resulted in preservation of transplanted lung tissue in respect to histopathological and biochemical findings.

Comparison of histopathological and biomechanical changes of ligamentum mucosum in patients with anterior cruciate ligament rupture.

OBJECTIVES: The aim of this study was to identify the biomechanical and histopathological changes of ligamentum mucosum (LM) in patients with intact versus ruptured anterior cruciate ligament (ACL). PATIENTS AND METHODS: A total of 67 patients (45 males, 22 females; mean age: 33.2±7.9 years; range, 18 to 45 years) who underwent arthroscopic knee surgery for intraarticular pathologies between July 2022 and January 2023 were prospectively analyzed. The patients with LM were divided into two groups as the ACL intact group (n=31) and ACL ruptured group (n=36). Biomechanical tests and histopathological examinations were performed in all LM patients. RESULTS: Age and body mass index distributions were similar between the groups (p>0.05). Peak force values of the LM in the ACL ruptured group were significantly higher than the ACL intact group (p=0.037). No significant difference was found between the groups in terms of collagen index (p=0.103) and fibroblast count (p=0.821). CONCLUSION: The peak force values of the LM were significantly higher in the ACL ruptured group as compared to the ACL intact group, which is probably due to the adaptation of LM in patients with ACL rupture against increased deforming forces to maintain knee stability.

Submandibular triangle masses.

OBJECTIVE: The study aims to analyze the demographic data of a large case series operated on because of submandibular triangle mass for more than 10 years and presents a review of the literature. MATERIALS AND METHODS: The charts of patients who underwent surgical intervention for submandibular triangle mass between January 2000 and November 2010 were reviewed. The medical history, age, sex, duration of symptoms, clinical presentation, preoperative investigations, and histopathologic diagnosis were reviewed. RESULTS: The study included 66 subjects; 12 patients (18.2%) with submandibular sialolithiasis, 18 patients (27.2%) with sialadenitis, 10 patients with lymphadenitis (15.1%), and 26 patients (39.3%) with tumors. Of the tumors, 23% was malignant and 77% was benign. Benign tumors of submandibular gland comprised 22.7% and malign tumors of submandibular gland comprised 3% of all submandibular mass. The most common benign tumor was pleomorphic adenoma. The most frequent histopathologic diagnoses of submandibular masses originated from the submandibular gland, and these comprised 71.2% of all submandibular mass pathologies. The main symptom was a painless mass. Ultrasonography was the most common preoperative diagnostic procedure. Fine-needle aspiration biopsy was performed in 26 patients. A clear diagnosis could not be provided in 3 (12%) patients. CONCLUSION: Infectious conditions and benign tumors are more frequent than malign tumors in the submandibular region. The histopathologic diagnoses mainly consisted of submandibular sialadenitis, sialolithiasis, pleomorphic adenoma, and lymphadenitis. Ultrasonography is the first option of radiologic evaluation. Fine-needle aspiration biopsy is a very useful and usually sufficient diagnostic procedure for histopathologic diagnosis. Excisional biopsy can be performed when the fine-needle aspiration biopsy failed.

Receptor Tyrosine Kinase Pathway and Infiltrating Urothelial Carcinoma.

Receptor tyrosine kinase pathway is frequently searched for cancer causing mutations in tumors. Emerging targeted therapies are gleam of hope for them. Infiltrating urothelial carcinoma can have many morphological aspects according to their differentiation/variants. To evaluate KRAS, BRAF, and PIK3CA mutations and HER2, EGFR, and p16 expression, we divided urothelial carcinomas into two groups: differentiated/variants (n = 12) and conventional (n = 12). We compared results with clinical, demographic, histopathologic features and survival rates. No statistically significant results could be obtained in the comparison of histopathologic properties/survival rates with mutation analysis and EGFR, HER2, and p16 status. Differentiated/variants urothelial carcinoma showed higher EGFR expression (P < 0.001). Glandular differentiation was the most frequent type, followed by squamous and sarcomatoid differentiation. We observed the most common mutation at KRAS with a propensity for urothelial carcinoma with glandular differentiation. More than one mutation/high protein expression was seen in some tumors. Targeted therapies for KRAS mutation can be effective at urothelial carcinoma with glandular differentiation. Heterologous expression of relevant proteins and genes can be a cause for targeted treatment obstacle. The determination of the molecular characters of tumors is a guide in creating targeted treatment algorithms and in choosing the patient.

Clinicopathologic Features and Prognostic Significance of Immunohistochemistry and In Situ Hybridization Based Molecular Classification in Gastric Carcinoma.

BACKGROUND/AIM: Gastric carcinoma (GC) is a highly heterogeneous disease with many subtypes that have different morphologic and molecular characteristics. In the current study, we analyzed immunohistochemical (IHC) and in situ hybridization (ISH) features of GCs and evaluated their association with prognosis and clinicopathological features. MATERIALS AND METHODS: Three hundred cases analyzed by IHC and ISH for microsatellite stability, p53, e-cadherin, HER2, PD-L1 expression, and Epstein-Barr virus (EBV) status. Cases were classified into five subgroups based on expression profile. The relationships between subgroups, clinicopathological features, and survival were determined. RESULTS: Ten (3.3%) cases were classified as EBV-associated, 45 (15%) as microsatellite instable (MSI), 73 (24.3%) as EBV-/microsatellite-stable (MSS)/epithelial-mesenchymal-transformation (EMT)-like, 75 (25%) as EBV-/MSS/ non-EMT-like/p53+, and 97 (32.3%) as EBV-/MSS/non-EMT-like/p53-. The MSI subtype had the best overall survival (OS). In contrast, the EBV-/MSS/EMT-like subtype had the poorest OS. The MSI subtype was also related with old age of the patient and antrum-corpus localized tumors, whereas the EBV-/MSS/EMT-like was associated with young age, larger tumor size, and advanced stage presentation. PD-L1 positivity is highly correlated with MSI and EBV-associated subtypes. CONCLUSION: Our data demonstrated a link between IHC/ISH characteristics of GC and clinical outcomes. IHC/ISH based molecular classification may be helpful in predicting the survival.

Dermatopathological Correlation of Clinically Challenging Cutaneous Lesions: a Single Center Experience of 2184 Cases.

Introduction: Although a trained eye can easily identify typical skin lesions, histopathological examination and clinicopathological correlation are critical in challenging cases. Objectives: The primary objective is to organize the final diagnoses reached following clinicopathological consensus in clinically challenging cutaneous lesions, identifying the most common diagnostic scenarios encountered by dermatopathologists and discussing their diverse differentials submitted by clinicians. The secondary objective is to investigate how the case profile and clinician decision-making processes evolved during the COVID-19 pandemic. Methods: Skin and mucosa samples collected by the dermatology department between 2016 and 2020 were classified based on pathology reports. For frequent diagnoses, preliminary diagnoses stated by clinicians on pathology requisition forms were reviewed. The years preceding and following the first nationally reported COVID-19 case were compared to investigate the pandemic's impact on the distribution of dermatology and dermatopathology cases. Results: One thousand nine hundred and eighty-nine reports were classified into 4 major categories: inflammatory (49.8%), neoplastic (30.1%), other diseases (7.1%), and non-diagnostic (12.8%). We further classified inflammatory diseases based on major tissue reaction patterns and neoplasms based on cell origin. We analyzed the leading diagnoses in each category, discussed their differential diagnoses, and provided clinicians with clues to reduce errors in practice. Following the pandemic, the overall number of pathology reports and patient admissions dropped dramatically, with significant changes in case profiles. Conclusions: We presented and discussed the frequently encountered confounding cases to sketch the diagnostic landscape. In the authors' experience, clinicopathological correlation can increase the rate of reaching the diagnosis by up to 75.3%.

STAT3, VEGF, and PSMA Expression Patterns in Malignant Peripheral Nerve Sheath Tumors, Malignant Melanomas, and Glioblastomas: Does Staining Percentage and Intensity Have an Effect on Survival?

Malignant peripheral nerve sheath tumors (MPNSTs), glioblastomas (GBMs), and malignant melanomas (MMs) are neural crest-originating aggressive tumors with a poor prognosis. Signal transducer and transcription activator 3 (STAT3) plays a role in many biological processes, including cell life and proliferation, the acute phase response, chronic inflammation, autoimmunity, metabolism, and cancer progression, It is also known to be a prooncogenic transcription factor. Vascular endothelial growth factor (VEGF) is one of the most potent proangiogenic stimuli ever identified. It mediates tumor neovascularization, and is associated with angiogenesis and lymphangiogenesis. The prostate-specific membrane antigen (PSMA) folate hydrolase I, despite its name, has been found in tissues other than the prostate. It is overexpressed in prostate cancer cells and several other cancers, and has the potential to be a target for radioligand therapy. We investigated the value of STAT3, VEGF and PSMA immunohistochemical expression patterns and their effects on survival in MPNSTs, GBMs, and MMs. Their expression patterns were evaluated in 25 MPNSTs, 27 GBMs, and 25 MM cases. All GBM cases stained positively for STAT3 and VEGF. In the other groups, the staining patterns were heterogeneous. None of the cases showed positive staining with PSMA. There was no statistically significant difference in survival between cases with differing VEGF and STAT3 staining patterns in the MPSNT and MM groups, but there was an increase in mortality as the VEGF score increased in the GBM group. The suppression of VEGF and STAT3 may be a promising avenue for treatment of MPNSTs, GBMs, and MMs, although further research is needed.

Diffuse-type giant cell tumor: Pigmented villonodular synovitis of patellar fat pad.

Pigmented villonodular synovitis (PVNS) is a rare, relatively benign intra-articular lesion characterized by slowly progressing proliferation of the synovial tissue. It is most commonly observed in the knee joint. Localized and diffuse types are two types of PVNS depending on the synovial involvement. Arthroscopic and excisional resections are recommended as the treatment methods for the PVNS. Radiotherapy or chemotherapy can be adjuvant therapeutic options for the widespread masses. In this study, we presented a case of diffuse PVNS originating from the patellar fat pad.

Rifaximine spacer application is not superior to local teicoplanin treatment in a rat model of osteomyelitis.

OBJECTIVE: Acute and chronic osteomyelitis generally require long-term antibiotic therapy and surgical debridement. Implant-associated osteomyelitis, particularly from methicillin-resistant Staphylococcus aureus (MRSA) strains, is difficult to treat. Rifaximin is an antibiotic derived from rifamycin which may be effective in the treatment of osteomyelitis in terms of its wide spectrum of action and pharmacological properties. The aim of this experimental study was to investigate the local efficacy of rifaximin in rat models with MRSA and implant associated osteomyelitis. METHODS: This study was carried out with 40 adult Wistar albino rats. The rats were randomly divided into 4 equal groups with 10 rats in each. An implant related MRSA osteomyelitis was created in the right tibia metaphysis of each rat by Norden's experimental osteomyelitis model. After 4 weeks, the implants of each tibia were removed and debridement was applied. Group 1 was designed as control group and no other treatment was applied other than debridement. Bone cement without any antibiotic was applied to Group 2, bone cement with teicoplanin was applied to Group 3 and bone cement with rifaximin was applied to Group 4. After 4 weeks from the second surgery, euthanasia was performed to the rats and the clinical, histopathological and microbiological results were compared. RESULTS: There was no statistically significant difference between the groups in clinical scoring. A statistically significant difference was found between the histopathological scores of Group 1 and Group 2 and the histopathological scores of Groups 3 and 4; the histopathological scores of Group 1 and Group 2 were found to be higher than Group 3 and Group 4. When the pre-and post-treatment colony numbers were compared, although there was a statistically significant difference between Group 3 and Group 2, no statistically significant difference was found between Group 4 and Group 1 results. CONCLUSION: In spite of its wide spectrum, the local efficacy of rifaximin in the treatment of osteomyelitis could not be demonstrated. This study shows the ability to shed light on some future comprehensive studies with the inclusion of infection markers.