Methods for diagnosing a cancer in a subject include providing a biological sample from the subject and determining an amount of Reg3A in the sample. The subject is then diagnosed as having cancer or a risk thereof if there is a measurable difference in the amount of the Reg3A in the biological sample as compared to a control level of the Reg3A. The amount of Reg3A can be determined by itself or in combination with an amount of soluble E-cadherin (sEcad) and/or additional Reg family members. The subject can further be administered an effective amount of an agent capable of affecting an expression level or activity of Reg3A as part of a therapeutic method for treating a cancer. The Reg3A affecting agent can be an anti-Reg3A antibody that is administered alone or with an effective amount of a chemotherapeutic agent.
