Non-injection-site fibrosarcoma in cats is a connective tissue cancer arising from fibroblasts — the cells that produce the structural fibrous framework of tissues. Unlike injection-site sarcoma (FISS), this form develops spontaneously without a known link to previous injections or vaccinations. It typically presents as a firm, progressive mass most commonly found on the head, limbs, or trunk. The tumour is locally invasive, growing along tissue planes in a manner that makes the true extent of disease larger than the palpable lump suggests. Surgical excision with wide margins is the treatment of choice, and radiation therapy can be a valuable adjunct when margins are incomplete. It is worth noting that the published evidence base for non-ISS feline fibrosarcoma is very limited, with only small case series available. Most treatment recommendations are extrapolated from FISS and canine STS data. Clinicians should discuss this evidence gap openly with owners.