Sounds like a Non-qualified stock option sale.
IF the "gain" on the sale of start-up stock is reflected on your W-2, you are supposed to update the cost basis on the 1099-B to be the same as it's full value as on the date of sale...thus no gain on the 1099-B transaction (or a slight loss due to brokerage fees).
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If it isn't related to NQSO stock sale, or disqualifying sale of ISO shares. Then you may have to explain some more, and perhaps someone more knowledgeable will be able to answer (as that would be beyond me)
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
