The subject invention pertains to novel materials and methods for use in treating patients afflicted with oncological disorders, such as tumors. One aspect of the invention concerns methods for treating tumors comprising the administration of drug loaded pH-sensitive microspheres to a patient in need of anticancer therapy. The pH-sensitive microspheres have a swelling transition with the pH range found in or near tumor tissue. When the microspheres swell, the loaded drug is released into the microenvironment of the tumor tissue. The subject invention also pertains to novel microspheres useful in the methods of the invention. The microspheres are capable of effectively releasing a loaded substance at a predetermined pH. The subject invention also concerns novel methods for synthesizing the microspheres of the present invention.