My sense is the lack of malignant cells from a fine needle aspiration may not rule out cancer in the surrounding area as the portion sampled is small.

But, with previous surgery, fluorodeoxyglucose (FDG) uptake and increasing CA 19-9, the doctors may be concerned, and hence want to do the one thing that might help. You mention chemo and radiation ... to be clear, was their recommendation chemotherapy (CHT) or chemotherapy radiation therapy (CRT)? The later usually includes oral chemo medicine with radiation.