6610 Background. Recent patterns-of-care studies report that cancer patients often do not complete prescribed therapy, with potentially important implications for clinical outcomes including survival. Yet, little is known about the frequency and determinants of early treatment discontinuation. The aims of this study were to address these issues in a largely rural population of a 33-county region of southwest Georgia. Methods. A total of 3,996 cases of breast, colorectal (CRC), lung, and prostate cancer diagnosed between 2001 and 2003 were identified from the Georgia Comprehensive Cancer Registry, with data collected from medical records by trained abstractors; 3,949 cases were available for analysis. Since completion of adjuvant chemotherapy with a goal of cure may be particularly important, this report focuses on cases treated for stage I and II breast cancer and stage III CRC. Results. Among 854 stage I-II breast cancer cases, 323 (38%) received chemotherapy. In 293 of those cases, treatment was stopped within the first year post-diagnosis. The primary reasons for stopping included treatment completion (86%), significant toxicity (8%), or other clinical reasons (2%). In only seven cases (2%) was treatment discontinued due to patient factors (e.g. refusal or did not return to clinic). Among 179 stage III CRC cases, 124 (69%) received adjuvant chemotherapy; in 117 cases chemotherapy was stopped within 12 months following diagnosis. Clinical reasons for stopping chemotherapy in those 117 cases included treatment completion (67%), toxicity (12%), disease progression (8%), or death (3%). In only 4% of cases was chemotherapy discontinued due to patient refusal, and in 3% of cases a patient was lost to follow up. Conclusions. In this largely rural population, only a small proportion of cases stopped adjuvant chemotherapy early due to patient-attributable factors; most treatment termination was due to clinical indications. Review of practice patterns using only administrative data may not reveal the actual reasons for treatment discontinuation. Further study of underlying factors of early termination is needed to design appropriate interventions to promote completion of prescribed therapy. No significant financial relationships to disclose.