Box 4 is Federal Tax Withholdings. When you say Box 4 is missing do you mean that Box 4 is blank? If so, is not unusual that Box 4 would be blank on a 1099-B. Typically, tax withholdings are not withheld from stock sale transactions. Unless you specifically requested withholdings from trades then it will be blank.
If you feel it is incorrect, I would contact customer services at E*TRADE to clarify.
