Infiltrative

Infiltrative is an adjective used in biology and medicine to describe a process by which cells, substances, or pathologic processes spread into surrounding tissues. It denotes invasion or permeation rather than the presence of a well-defined, encapsulated mass. The term comes from infiltrate, from Latin infiltrare, meaning to seep in or creep in.

In oncology, an infiltrative or invasive growth pattern means cancer cells extend beyond the primary lesion into adjacent tissue. This often yields irregular, poorly defined margins and complicates complete surgical removal or radiotherapy. Examples include infiltrating ductal carcinoma of the breast and glioblastoma, where tumor cells infiltrate along normal tissue planes. Infiltration can occur via lymphatics or nerves (perineural invasion) and correlates with prognosis.

In pathology, the word infiltrate is also used for aggregates of inflammatory cells within tissue, such as neutrophilic, lymphocytic, or eosinophilic infiltrates, seen in various infections, autoimmune diseases, or hypersensitivity reactions. The pattern and composition of an infiltrate help diagnose the underlying process and stage disease activity.

Outside tumors, infiltrative describes diseases in which abnormal substances accumulate within an organ, changing its structure and function. Examples include infiltrative cardiomyopathy (amyloid, sarcoid, iron overload) and other storage diseases. In radiology, infiltrative processes produce ill-defined, diffuse involvement on imaging, reflecting tissue invasion rather than discrete nodules.