Pathology
On gross examination, IF tumors are typically white-yellow masses with central necrosis (i.e. areas of dead or dying cells), and areas containing cysts  and/or old, dried hemorrhages. The tumors are often poorly circumscribed, have an infiltrative appearance, may be multinodular, and lie in subcutaneous tissue but may also involve the dermal layer of the skin and/or the reticular dermis. Microscopic histopathological studies of IF tissues report the characteristic presence of a distinct zonal appearance, i.e. the presence of central zones of fibrinoid necrosis and areas of cyst-laden necrosis in a hypocellular background surrounding by a zone of granulation tissue (i.e. connective tissue containing microscopic blood vessels) populated by atypical, swollen fibroblasts, myofibroblasts, and/or macrophages.Immunohistochemistry analyses of IF tumors often show the presence of fibroblasts, fibroblast-like cells, and or other types of cells that in a percentage of cases express smooth muscle actin proteins, CD68 protein,. desmin protein, vimentin protein, and collagen type IV protein, but not keratin, S100, calponin, or CD34 proteins. The finding that a tumors cells have some of these patterns of protein expression can help support the diagnosis of IF. Gene and chromosome abnormalities
A single case of IF was found to have tumor cells bearing chromosomal translocations between chromosomes 1 and 2 and/or chromosomes 7 and 19. While further studies are needed to confirm these finding and to conduct further gene and chromosome analyses, these results support the notion that IF tumors are neoplasms rather than purely reactive lesions.
Sitagliptin/simvastatin, sold under the brand name Juvisync, is a fixed-dose combination anti-diabetic medication used to treat type 2 diabetes and hypercholesterolemia. It contains sitagliptin and simvastatin. Sitagliptin is a dipeptidyl peptidase-4 inhibitor  and simvastatin is an HMG-CoA reductase inhibitor. These two disorders commonly occur in people at the same time, and have been typically treated with administration of these medications separately. The combination was approved in 2011, and sold under the brand name Juvisync by Merck. Juvisync was later removed from the market in 2013, due to business reasons. History
In 1991, Merck & Cos simvastatin was approved as an HMG-COA inhibitor to lower the levels of LDL cholesterol. In 2006, Merck & Cos sitagliptin was approved by the FDA for treatment of diabetes mellitus type 2. Regulation
Juvisync was the first product to combine a cholesterol lowering drug with a type 2 diabetes drug in the same tablet. Nonclinical toxicology
Sitagliptin: Using male and female rats, a two-year carcinogenicity study was carried out with doses of 50, 150, and 500 mg/kg/day. The 500 mg/kg dose has exposure limits of 60 times what would be seen in the highest dose in humans. At this dose, liver adenoma/carcinoma was seen. Tumors were not seen from the smaller doses. Nomutagenic or clastogenic effects were seen from tests using several assays (CHO, rat, etc.). Fertility studies in rats showed no teratogenic effects.Simvastatin: No tumorigenic effect was seen in a 72-week carcinogenicity study using mice at the low dose levels.