Cook pasta in a large pot of generously salted boiling water until al dente. Reserve 1/2 cup pasta water; drain pasta and return to pot.
Meanwhile, slice corn kernels from cobs into a shallow bowl, then scrape corn "milk" from cobs with the side of a spoon. Melt butter in a small saucepan over medium-high. Reduce heat to medium and simmer until butter browns, about 7 minutes. Add corn and corn milk; simmer just until corn is crisp-tender, about 30 seconds.
Add corn mixture to pasta with tuna in oil and tomatoes; toss to combine. Season with salt and pepper. Add reserved pasta water, a little at a time, until sauce evenly coats pasta. Let cool 10 minutes. Gently fold in arugula. Serve, with lemon wedges.