Flooring Tile - Cutting Cultured Marble.

I am replacing a 30 year old undermount bathroom sink with a new drop in porcelain. The countertop is that old cultured marble which because of the size of it, is too expensive to replace at this time. The problem is I need to cut the inside diameter of the old hole by about 1 inch for the new sink to fit.
Can I cut this myself? What tools and how exact would one have to be? Thanks for any advice.

not an expert in this but I think if you cut it you will also need to polish it to get a smooth finish. 1 inch doe not sound like a lot - why not leave it as an overhang

Sorry, I need to clarify, the new sink is a drop in the top and the hole isn't big enough.

Sorry, I need to clarify, the new sink is a drop in the top and the hole isn't big enough.

ok then it is not undermount? then you dont need a smooth finish on the edge since it will be covered. I would then be more worried about making such old marble narrower near the edges - normally these are reinforce with metal laid in the marble. Why not go with another undermount

I can't get the exact size. Since its so old, they don't make that size sink anymore. I went to local plumbing supply and the closest size is a top mount but still a little larger than the hole already cut.

Measure the size of the opening to the existing sink. A drop in sink will have a 'lip' and will cover the hole that you cut out. It takes a masonry saw to cut cultured marble. Have you compared the price of a drop in sink at a home center to the cost of another cultured marble top, plus your time and labor to cut out the sink opening? You will have to disconnect the plumbing either way you go. And, you will want to eventually replace the cultured marble top anyway. Custom sized cultured marble tops do tend to cost more than standard size. Let's say the new cultured marble top will cost $200 and it will last 20 years. That's just $10/year. A drop in sink in a cultured marble top may produce less than satisfactory results.