Inflammatory fibroid polyps of the colon: a study on the morphological spectrum, immunoexpression characteristics, and outcomes

Colonic inflammatory fibroid polyps (IFPs) have not been extensively studied. In this study, we collected nine cases of colonic IFPs and provide a comprehensive description of the clinicopathological features and developmental outcomes of these lesions. These nine cases of colonic IFPs can be classified into four types on the basis of their pathological characteristics: early-stage, classic, inflammatory, and sclerotic. The early-stage type of IFP is characterized by the deposition of fibrosis around blood vessels and between glands. The classic type of IFP is easily identifiable by its “onion-skin-like” structure; however, immunohistochemical (IHC) staining for CD34 may demonstrate focal positivity or even negativity. The inflammatory type of IFP is large and characterized by significant infiltration of plasma cells. IHC staining revealed variable positivity for both CD34 and PDGFRα across different regions of the lesions. The sclerotic type of IFP is characterized by substantial deposition of collagen. Furthermore, our findings suggest that early-stage IFPs have the potential to either develop into classic-type IFPs or degenerate into sclerotic-type IFPs. Additionally, classic-type IFPs may acquire PDGFRα mutations and ultimately transform into inflammatory-type IFPs. Colonic IFPs exhibit a distinct morphological spectrum and unique immunoexpression characteristics as they progress. Only inflammatory-type and classic-type IFPs with PDGFRα mutations or immunoexpression should be regarded as genuine neoplastic lesions.