especially pleasing has been the large increase in our sales

especially pleasing has been the large increase in our sales abroad.这句话是什么意思.
为什么pleasing是形容词却做了主语?
全文是 This year the company has experienced a remarkable increase in demand for most of its products.In general the demand for stationery has shown the biggest increase for many years.Especially pleasing has been the large increase in our sales abroad.