By Eric Martin -- Roche Diagnostics, the world's sixth-largest drug firm, said it plans to eliminate 140 back-office jobs at its U.S. headquarters in Indianapolis. But the company said Tuesday that it will replace the positions with new hires in other job classifications by the end of the year. The laid-off employees represent a small fraction of the 3,500 Roche workers at the 18-building U.S. headquarters campus. They work in human resources, information technology and communications. The company expects to hire about the same number of people in manufacturing, sales and marketing positions. The decision was announced to employees earlier this month.