0001528621-15-003995.hdr.sgml : 20151209 20151209145655 0001528621-15-003995 487 6 20151209 20151209 20151209 Invesco Unit Trusts Taxable Income Series 538 0001608172 000000000 487 33 333-206149 151278216 3500 LACEY DRIVE DOWNERS GROVE IL 60515 212-652-4344 3500 LACEY DRIVE DOWNERS GROVE IL 60515