How long can mantle cell lymphoma go undetected? where does mantle cell lymphoma show up?

A few months: We obviously don't know the natural history of such a malignancy, but suspect it is usually an aggressive process that will be clinically diagnosable within months of onset by manifesting symptoms. As implied enlargement of lymph nodal areas will be the presentation in most cases.

Months, anywhere: Mantle cell lymphoma is a rare subtype of non-hodgkin's lymphoma. It usually grows relatively slowly and might take several weeks to a few months to develop. It most commonly presents in the lymph nodes, the blood, and the spleen although it can also present anywhere in the G.I. Tract from the stomach down to the colon.