Adherence Outcomes and Risk Factors Predicting Nonadherence to Active Surveillance in Patients With Stage 1 Testicular Germ Cell Tumors.

PURPOSE: Adherence to active surveillance in patients with stage 1 testicular cancers may be influenced by factors affecting capacity and motivation to attend appointments. The aims of this study were to assess adherence to active surveillance and analyze factors which may impact adherence. PATIENTS AND METHODS: A retrospective cohort study was conducted in patients diagnosed with stage 1 testicular cancer between 2005 and 2020, and managed with active surveillance at 3 institutions in South Western Sydney, Australia. Adherence with active surveillance was followed to 2023 and patients were subsequently classified into 3 groups: "Optimal," "Adequate" or "Loss to follow-up" (LTFU). Factors for adherence were analyzed using multivariable logistic regression. Disease recurrence was analyzed using multivariable Cox regression. RESULTS: In 125 patients, adherence with active surveillance was assessed as "Optimal" in 64 (51%), "Adequate" in 14 (11%), and LTFU in 47 (38%). Multivariable analysis demonstrated that patients had higher odds of being in the "Optimal" or "Adequate" categories if they were from a culturally and linguistically diverse background (OR 4.86, P = .026), nonsmokers (OR 7.63, P = .0002), not employed (OR 4.93, P = .0085), had a partner (OR 2.74, P = .0326), or were diagnosed after June 2016 (OR 5.22, P = .0016). Recurrence occurred in 21 patients (17%). The risk of recurrence increased with the presence of multiple pathological risk factors (HR 5.77, P = .0032), if patients were unemployed (HR 2.57, P = .032), or if they had "Optimal" or "Adequate" adherence (HR 12.74, P = .0136). CONCLUSION: Adherence with active surveillance was poorer in this cohort of stage 1 testicular cancer patients. Patients from culturally and linguistically diverse backgrounds and those who were nonsmokers, unemployed, with a partner, and later date of diagnosis, were more likely to be adherent with active surveillance.

Hidden in plain sight - Survival consequences of baseline symptom burden in women with recurrent ovarian cancer.

OBJECTIVE: To describe the baseline symptom burden(SB) experienced by patients(pts) with recurrent ovarian cancer(ROC) prior and associations with progression free survival (PFS) and overall survival (OS). METHODS: We analysed baseline SB reported by pts. with platinum resistant/refractory ROC (PRR-ROC) or potentially­platinum sensitive ROC receiving their third or greater line of chemotherapy (PPS-ROC≥3) enrolled in the Gynecologic Cancer InterGroup - Symptom Benefit Study (GCIG-SBS) using the Measure of Ovarian Symptoms and Treatment concerns (MOST). The severity of baseline symptoms was correlated with PFS and OS. RESULTS: The 948 pts. reported substantial baseline SB. Almost 80% reported mild to severe pain, and 75% abdominal symptoms. Shortness of breath was reported by 60% and 90% reported fatigue. About 50% reported moderate to severe anxiety, and 35% moderate to severe depression. Most (89%) reported 1 or more symptoms as moderate or severe, 59% scored 6 or more symptoms moderate or severe, and 46% scored 9 or more symptoms as moderate or severe. Higher SB was associated with significantly shortened PFS and OS; five symptoms had OS hazard ratios larger than 2 for both moderate and severe symptom cut-offs (trouble eating, vomiting, indigestion, loss of appetite, and nausea; p < 0.001). CONCLUSION: Pts with ROC reported high SB prior to starting palliative chemotherapy, similar among PRR-ROC and PPS-ROC≥3. High SB was strongly associated with early progression and death. SB should be actively managed and used to stratify patients in clinical trials. Clinical trials should measure and report symptom burden and the impact of treatment on symptom control.

Patients' perception of the benefits of palliative systemic therapy for advanced cancer.

BACKGROUND: Patients with advanced cancer who misunderstand their prognosis and chance of cure tend to overestimate the likely benefits of palliative systemic therapy. AIM: To determine patient perceptions of palliative systemic therapy benefits in advanced cancer. METHODS: We surveyed 104 outpatients with advanced cancer receiving systemic anticancer therapy and their treating oncologists. Patients recorded their understanding of treatment impact on chance of cure and symptoms. Life expectancy was estimated by patients and oncologists. A visual analogue scale (0-10) was used to record how patients and oncologists valued quality of life (QOL) and length of life (LOL) (<4 QOL most important; 4-7 QOL and LOL equal; >7 LOL most important). Patient-oncologist discordance was defined as a ≥4-point difference. RESULTS: The main reasons patients selected for receiving treatment were to live longer (54%) and cure their cancer (36%). Most patients reported treatment was very/somewhat likely to prolong life (84%) and improve symptoms (76%), whereas 20% reported treatment was very/somewhat likely to cure their cancer. 42% of patients selected a timeframe for life expectancy (choice of four timeframes between <1 year and ≥5 years); of these, 62% selected a longer timeframe than their oncologist. When making treatment decisions, 71% of patients (52% of oncologists) valued QOL and LOL equally. Patient-oncologist discordance was 21%, mostly because of oncologists valuing QOL more than their patients (70%). CONCLUSION: At least 20% of patients receiving systemic therapy for advanced cancer reported an expectation of cure. Most patients and oncologists value QOL and LOL equally when making treatment decisions.

A phase II trial of nivolumab followed by ipilimumab and nivolumab in advanced non-clear-cell renal cell carcinoma.

OBJECTIVE: To evaluate the efficacy of sequential treatment with ipilimumab and nivolumab following progression on nivolumab monotherapy in individuals with advanced, non-clear-cell renal cell carcinoma (nccRCC). MATERIALS AND METHODS: UNISoN (ANZUP1602; NCT03177239) was an open-label, single-arm, phase 2 clinical trial that recruited adults with immunotherapy-naïve, advanced nccRCC. Participants received nivolumab 240 mg i.v. two-weekly for up to 12 months (Part 1), followed by sequential addition of ipilimumab 1 mg/kg three-weekly for four doses to nivolumab if disease progression occurred during treatment (Part 2). The primary endpoint was objective tumour response rate (OTRR) and secondary endpoints included duration of response (DOR), progression-free (PFS) and overall survival (OS), and toxicity (treatment-related adverse events). RESULTS: A total of 83 participants were eligible for Part 1, including people with papillary (37/83, 45%), chromophobe (15/83, 18%) and other nccRCC subtypes (31/83, 37%); 41 participants enrolled in Part 2. The median (range) follow-up was 22 (16-30) months. In Part 1, the OTRR was 16.9% (95% confidence interval [CI] 9.5-26.7), the median DOR was 20.7 months (95% CI 3.7-not reached) and the median PFS was 4.0 months (95% CI 3.6-7.4). Treatment-related adverse events were reported in 71% of participants; 19% were grade 3 or 4. For participants who enrolled in Part 2, the OTRR was 10%; the median DOR was 13.5 months (95% CI 4.8-19.7) and the median PFS 2.6 months (95% CI 2.2-3.8). Treatment-related adverse events occurred in 80% of these participants; 49% had grade 3, 4 or 5. The median OS was 24 months (95% CI 16-28) from time of enrolment in Part 1. CONCLUSIONS: Nivolumab monotherapy had a modest effect overall, with a few participants experiencing a long DOR. Sequential combination immunotherapy by addition of ipilimumab in the context of disease progression to nivolumab in nccRCC is not supported by this study, with only a minority of participants benefiting from this strategy.

Patient-Reported Outcomes in Ovarian Cancer: Facilitating and Enhancing the Reporting of Symptoms, Adverse Events, and Subjective Benefit of Treatment in Clinical Trials and Clinical Practice.

Patient-reported outcomes (PROs) provide a valid, standardized way of assessing symptoms, adverse events and the subjective benefit of treatment from the patient's perspective. Assessment of PROs is critical in ovarian cancer due to the high morbidity of the disease and its treatments. Several well-validated PRO measures are available to assess PROs in ovarian cancer. Their inclusion in clinical trials can provide evidence on the benefits and harms of new treatments based on patients' experiences to guide improvements in clinical practice and health policy. Aggregate PRO data collected in clinical trials can be used to inform patients about likely treatment impacts and assist them to make informed treatment decisions. In clinical practice, PRO assessments can facilitate monitoring of a patient's symptoms throughout treatment and follow-up to guide their clinical management; in this context, an individual patient's responses can facilitate communication with their treating clinician about troublesome symptoms and their impact on their quality of life. This literature review aimed to provide clinicians and researchers with a better understanding of why and how PROs can be incorporated into ovarian cancer clinical trials and routine clinical practice. We discuss the importance of assessing PROs throughout the ovarian cancer disease and treatment trajectory in both clinical trials and clinical practice, and provide examples from existing literature to illustrate the uses of PROs as the goals of treatment change in each setting.

Measure of Ovarian Symptoms and Treatment concerns (MOST) indexes and their associations with health-related quality of life in recurrent ovarian cancer.

PURPOSE: The Measure of Ovarian Symptoms and Treatment (MOST) concerns is a validated patient-reported symptom assessment tool for assessing symptom benefit and adverse effects of palliative chemotherapy in women with recurrent ovarian cancer (ROC). We aimed to examine (i) how symptoms within MOST symptom indexes track together (i.e. co-occur) and (ii) the association between MOST symptom indexes and key aspects of health-related quality of life (HRQL). METHOD: A prospective cohort of women with ROC completed the MOST-T35, EORTC QLQ-C30 and EORTC QLQ-OV28 at baseline and before each cycle of chemotherapy. Analyses were conducted on baseline and end-of-treatment data. Exploratory factor analysis and hierarchical cluster analysis identified groups of co-occurring symptoms. Path models examined associations between MOST symptom indexes and HRQL. RESULTS: Data from 762 women at baseline and 681 at treatment-end who completed all 22 symptom-specific MOST items and at least one HRQL measure were analysed. Four symptom clusters emerged at baseline and treatment-end: abdominal symptoms, symptoms associated with peripheral neuropathy, nausea and vomiting, and psychological symptoms. Psychological symptoms (MOST-Psych) and symptoms due to disease (ovarian cancer) or treatment (MOST-DorT) were associated with poorer scores on QLQ-C30 and OV28 functioning domains and worse overall health at both time points. CONCLUSION: Four MOST symptom clusters were consistent across statistical methods and time points. These findings suggest that routine standardized assessment of psychological and physical symptoms in clinical practice with MOST plus appropriate symptom management referral pathways is an intervention for improving HRQL that warrants further research.

Symptom burden and quality of life with chemotherapy for recurrent ovarian cancer: the Gynecologic Cancer InterGroup-Symptom Benefit Study.

OBJECTIVE: The Gynecologic Cancer InterGroup (GCIG)-Symptom Benefit Study was designed to evaluate the effects of chemotherapy on symptoms and health-related quality of life (HRQL) in women having chemotherapy for platinum resistant/refractory recurrent ovarian cancer (PRR-ROC) and potentially platinum sensitive with ≥3 lines of chemotherapy (PPS-ROC ≥3). METHODS: Participants completed the Measure of Ovarian Cancer Symptoms and Treatment (MOST) and European Organization for Research and Treatment of Cancer (EORTC) Quality of Life Questionnaire QLQ-C30 questionnaires at baseline and every 3-4 weeks until progression. Participants were classified symptomatic if they rated ≥4 of 10 in at least one-third of symptoms in the MOST index. Improvement in MOST was defined as two consecutive scores of ≤3 in at least half of the symptomatic items at baseline. Improvement in HRQL was defined as two consecutive scores ≥10 points above baseline in the QLQ-C30 summary score scale (range 0-100). RESULTS: Of 948 participants enrolled, 910 (96%) completed baseline questionnaires: 546 with PRR-ROC and 364 with PPS-ROC ≥3. The proportions of participants symptomatic at baseline as per MOST indexes were: abdominal 54%, psychological 53%, and disease- or treatment-related 35%. Improvement was reported in MOST indexes: abdominal 40%, psychological 35%, and disease- or treatment-related 38%. Median time to improvement in abdominal symptoms occurred earlier for PRR-ROC than for PPS-ROC ≥3 (4 vs 6 weeks, p=0.044); median duration of improvement was also similar (9.0 vs 11.7 weeks, p=0.65). Progression-free survival was longer among those with improvement in abdominal symptoms than in those without (median 7.2 vs 2.5 months, p<0.0001). Improvements in HRQL were reported by 77/448 (17%) with PRR-ROC and 61/301 (20%) with PPS-ROC ≥3 (p=0.29), and 102/481 (21%) of those with abdominal symptoms at baseline. CONCLUSION: Over 50% of participants reported abdominal and psychological symptoms at baseline. Of those, 40% reported an improvement within 2 months of starting chemotherapy. Approximately one in six participants reported an improvement in HRQL. Symptom monitoring and supportive care is important as chemotherapy palliated less than half of symptomatic participants.

PI3K/AKT/mTOR inhibitors for advanced or recurrent endometrial cancer.

BACKGROUND: Endometrial cancer is one of the most common gynaecological cancers in developed countries. Treatment of advanced endometrial cancer usually involves radiotherapy, chemotherapy, endocrine therapy or a combination of these. However, survival outcomes are poor in advanced or metastatic disease. Better systemic treatment options are needed to improve survival and safety outcomes for these women. The PI3K/AKT/mTOR pathway is a frequently altered signalling pathway in endometrial cancer. Single-arm studies have reported some encouraging results of the PI3K/AKT/mTOR inhibition in advanced or recurrent endometrial cancer. OBJECTIVES: To assess the efficacy and safety of PI3K/AKT/mTOR inhibitor-containing regimens in women with locally-advanced, metastatic or recurrent endometrial cancer. SEARCH METHODS: We searched the Cochrane Central Register of Controlled Trials, MEDLINE and Embase to 16 January 2019; and the World Health Organization's International Clinical Trials Registry Platform (WHO ICTRP) and ClinicalTrials.gov in July 2018. We also reviewed reference lists from included studies and endometrial cancer guidelines. SELECTION CRITERIA: We included randomised controlled trials (RCTs) comparing a regimen with a PI3K/AKT/mTOR inhibitor (either alone or in combination with other treatments, such as chemotherapy or hormonal therapy) versus a comparator regimen without a PI3K/AKT/mTOR inhibitor. There were no restrictions on which comparator(s) were included. DATA COLLECTION AND ANALYSIS: We extracted data independently, and assessed risks of bias and the certainty of the evidence. The primary outcome measures were progression-free survival and toxicity (grade 3/4 where available). We derived hazard ratios (HRs) for time-to-event outcomes and risk ratios (RRs) for dichotomous outcomes. Secondary outcomes included overall survival, objective tumour response rate, quality of life and treatment-related death. We used GRADEproGDT to assess the certainty of the evidence for the most important outcomes (by first-line and second/third-line therapy for progression-free survival and overall survival). MAIN RESULTS: We included two RCTs involving 361 women. One study assessed the effects of the mTOR inhibitor temsirolimus, in combination with carboplatin/paclitaxel versus carboplatin/paclitaxel and bevacizumab in treatment-naïve women with advanced or recurrent endometrial cancer. The second study compared the mTOR inhibitor ridaforolimus alone versus progestin or investigator choice of chemotherapy in women who had received prior treatment for metastatic or recurrent endometrial cancer. We identified five ongoing studies on the effects of PI3K and AKT inhibitors, metformin and dual mTOR inhibitors.For first-line therapy, an mTOR inhibitor-containing regimen may worsen progression-free survival (HR 1.43, 95% CI 1.06 to 1.93; 1 study, 231 participants; low-certainty evidence), while for second/third-line therapy, an mTOR inhibitor probably improves progression-free survival compared to chemotherapy or endocrine therapy (HR 0.53, 95% CI 0.31 to 0.91; 1 study, 95 participants; moderate-certainty evidence). Data on toxicity were available from both studies: administering an mTOR inhibitor regimen may increase the risk of grade 3/4 mucositis (RR 10.42, 95% CI 1.34 to 80.74; 2 studies, 357 participants; low-certainty evidence), but may result in little to no difference in risk of anaemia or interstitial pneumonitis (low-certainty evidence for both toxicities). Overall, event rates were low. For first-line therapy, an mTOR inhibitor-containing regimen may result in little to no difference in overall survival compared to chemotherapy (HR 1.32, 95% CI 0.98 to 1.781 study, 231 participants; low-certainty evidence). The finding was similar for second/third-line therapy (HR 1.06, 95% CI 0.70 to 1.61; 1 study, 130 participants; low-certainty evidence). Administering mTOR inhibitor-containing regimens may result in little to no difference in tumour response compared to chemotherapy or hormonal therapy in first-line or second/third-line therapy (first line: RR 0.93, 95% CI 0.75 to 1.17; 1 study, 231 participants; second/third line: RR 0.22, 95% CI 0.01 to 4.40; 1 study, 61 participants; low-certainty evidence).Neither study collected or reported quality-of-life data. AUTHORS' CONCLUSIONS: Two RCTs have been reported to date, with low certainty of evidence. In a recurrent disease setting, mTOR inhibitors may result in improved progression-free survival, but we found no clear benefit in overall survival or tumour response rate. We await the publication of at least five ongoing studies investigating the role of PI3K/AKT/mTOR inhibitors in advanced or recurrent endometrial cancer before any conclusions can be drawn on their use.

Effect Sizes Hypothesized and Observed in Contemporary Phase III Trials of Targeted and Immunological Therapies for Advanced Cancer.

BACKGROUND: We sought to compare the effect sizes hypothesized in the trial design, observed in the trial results, and considered clinically meaningful by the American Society of Clinical Oncology (ASCO) 2014 recommendations, in phase III trials of targeted and immunological therapies. METHODS: We studied phase III, superiority trials of targeted and immunological therapies in advanced cancers published from 2005 to 2015. We recorded the characteristics, design parameters, and observed results for the primary endpoint of each trial. The effect sizes hypothesized in the trial design were compared with the ASCO 2014 recommendation that phase III trials be designed to detect overall survival (OS) benefits that are clinically meaningful (hazard ratio ≤0.8). RESULTS: All critical elements of the trial design (effect sizes hypothesized, estimated survival in the control group, power, and significance level) were identified in 165 of 213 included trials (77%). Of trials with a statistically significant result for the primary endpoint, 16 of 30 (53%) with a primary endpoint of OS and 20 of 53 (38%) with a primary endpoint of progression free survival (PFS) had an observed effect size less extreme than hypothesized; and 7 of 30 trials (23%) reported an observed effect size for OS that was statistically significant but not clinically meaningful (HR > 0.80) according to the ASCO 2014 recommendations. CONCLUSION: Many trials were designed such that an observed benefit in OS or PFS that was not clinically meaningful would be statistically significant. Phase III trials should be designed to provide results that are statistically significant for observed effects that are clinically meaningful but not for observed results that are of dubious clinical importance.

Validation of the modified Glasgow Prognostic Score (mGPS) in recurrent ovarian cancer (ROC) - Analysis of patients enrolled in the GCIG Symptom Benefit Study (SBS).

BACKGROUND: Modified Glasgow Prognostic Score (mGPS) is predictive of survival in many advanced cancers, but has not been evaluated in recurrent ovarian cancer (ROC). The aim was to determine validity of mGPS in ROC, investigate its associations with health related quality of life (HRQL) and ECOG performance status (PS). METHODS: mGPS is based on serum C reactive protein (CRP) and albumin, with scores ranging from 0 (least) to 2 (most). HRQL was measured with EORTC QLQ C-30 and OV-28. χ2 tests for trend were used to examine the relationship between HRQL, PS and mGPS. Cox proportional hazards regression was used to assess associations between mGPS, HRQL, clinicopathological factors, and overall survival (OS). RESULTS: Inflammatory markers were available in 516 of 948 patients in GCIG SBS. 200(39%) had potentially platinum sensitive ROC with ≥3 lines of chemotherapy, 316(61%) had platinum resistant ROC. 282(55%), 123(24%), 111(22%) had mGPS of 0, 1, 2, respectively. Median OS (months) was 18.1, 9.6, and 6.6 for mGPS 0, 1, and 2 respectively. mGPS was an independent predictor of OS after adjusting for PS and platinum sensitivity (p<0.001). mGPS remained a predictor of OS after adjusting for physical function, role function, global health status, abdominal/GI symptoms, and multiple clinicopathologic factors (p=0.02). Worse PS and higher mGPS were associated with poorer HRQL (p<0.001). Higher mGPS was associated with worse HRQL, independent of PS. CONCLUSION: The mGPS is an independent predictor of OS in ROC after adjusting for HRQL and clinicopathological factors. Higher mGPS is associated with worse HRQL independent of PS. mGPS is simple, inexpensive and may be suitable for clinical practice, clinical trial patient selection and stratification.

Reducing Uncertainty: Predictors of Stopping Chemotherapy Early and Shortened Survival Time in Platinum Resistant/Refractory Ovarian Cancer-The GCIG Symptom Benefit Study.

BACKGROUND: Clinicians and patients often overestimate the benefits of chemotherapy, and overall survival (OS), in platinum resistant/refractory ovarian cancer (PRROC). This study sought to determine aspects of health-related quality of life and clinicopathological characteristics before starting chemotherapy that were associated with stopping chemotherapy early, shortened survival, and death within 30 days of chemotherapy. MATERIALS AND METHODS: This study enrolled women with PRROC before starting palliative chemotherapy. Health-related quality of life was measured with EORTC QLQ-C30/QLQ-OV28. Chemotherapy stopped within 8 weeks of starting was defined as stopping early. Logistic regression was used to assess univariable and multivariable associations with stopping chemotherapy early and death within 30 days of chemotherapy; Cox proportional hazards regression was used to assess associations with progression-free and OS. RESULTS: Low baseline global health status (GHS), role function (RF), physical function (PF), and high abdominal/gastrointestinal symptom (AGIS) were associated with stopping chemotherapy early (all p < .007); low PF and RF remained significant after adjusting for clinicopathological factors (both p < .0401). Most who stopped chemotherapy early had Eastern Cooperative Oncology Group Performance Score 0-1 at baseline (79%); PF, RF, and GHS remained independently significant predictors of stopping chemotherapy early in this subgroup. Death within 30 days of chemotherapy occurred in 14%. Low GHS, RF, and PF remained significantly associated with death within 30 days of chemotherapy after adjusting for clinicopathological factors (all p < .012). CONCLUSION: Women with low GHS, RF, or PF before starting chemotherapy were more likely to stop chemotherapy early, with short OS. Self-ratings of GHS, RF, and PF could improve patient-clinician communication regarding prognosis and help decision-making in women considering chemotherapy for PRROC. IMPLICATIONS FOR PRACTICE: Measuring aspects of health-related quality of life when considering further chemotherapy in platinum resistant/refractory ovarian cancer (PRROC) could help identify women with a particularly poor prognosis who are unlikely to benefit from chemotherapy and could therefore be spared unnecessary treatment and toxicity in their last months of life. Self-ratings of global health status, role function, and physical function could improve patient-clinician communication regarding prognosis and help decision-making in women considering chemotherapy for PRROC.

Clinical Equipoise for Trials of Novel Biologic Therapies, Therapeutic Success Rates, and Predictors of Success: A Meta-Analysis.

PURPOSE: The demand for more rapid access to novel biologic therapies than randomized controlled trials can deliver is a topic of ongoing study and debate. We aimed to inform this debate by estimating therapeutic success from phase III trials comparing novel biologic therapies with standard of care and identifying predictors of success. METHODS: This was a meta-analysis of phase III trials evaluating novel biologic therapies in advanced breast, colorectal, lung, and prostate cancers. Therapeutic success was defined as statistically significant results for the primary end point favoring novel biologic therapies. RESULTS: Of 119 included phase III trials (76,726 patients), therapeutic success was 41%, with a statistically significant relative reduction in disease progression and death for novel biologic therapies over standard of care of 20% and 8%. Therapeutic success did not improve over time (pre-2010, 33%; 2010 to 2014, 44%; P = .2). Predictors of success were a biomarker-selected population (odds ratio, 4.74; 95% CI, 2.05 to 10.95) and progression-free survival end point compared with overall survival (odds ratio, 5.22; 95% CI, 2.41 to 11.39). Phase III trials with a biomarker-selected population showed a larger 28% progression-free survival benefit than phase III trials overall (hazard ratio, 0.72; 95% CI, 0.70 to 0.75) but similar 8% overall survival benefit (hazard ratio, 0.92; 95% CI, 0.90 to 0.94). Therapeutic success of phase III trials with and without a preceding phase II trial were 43% and 30%, respectively. CONCLUSION: Therapeutic success of novel biologic therapies in phase III trials, including therapies with a matching predictive biomarker, was modest and has not significantly improved over time. Equipoise remains and supports the ongoing ethical and scientific requirement for phase III randomized controlled trials to estimate treatment efficacy and assess the value of potential biomarkers.

The Impact of Mismatch Repair Status in Colorectal Cancer on the Decision to Treat With Adjuvant Chemotherapy: An Australian Population-Based Multicenter Study.

BACKGROUND: Testing for mismatch repair (MMR) status in colorectal cancer (CRC) may provide useful prognostic and predictive information. We evaluated the impact of such testing on real-world practice regarding adjuvant chemotherapy for patients with resected CRC. PATIENTS AND METHODS: A total of 175 patients with stage II and III mismatch repair-deficient (MMRD) CRC were identified from an Australian population-based study of incident CRCs. Their treatment decisions were compared with those for a cohort of 773 stage-matched patients with mismatch repair-proficient (MMRP) CRCs. The effect of MMR status, age, and pathologic characteristics on treatment decisions was determined using multiple regression analysis. RESULTS: Overall, 32% of patients in stage II and 71% of patients in stage III received adjuvant chemotherapy. Among the stage II patients, those with MMRD cancer were less likely to receive chemotherapy than were MMRP cases (15% vs. 38%; p < .0001). In this group, the treatment decision was influenced by age, tumor location, and T stage. MMR status influenced the treatment decision such that its impact diminished with increasing patient age. Among patients with stage III tumors, no difference was found in the chemotherapy rates between the MMRD and MMRP cases. In this group, age was the only significant predictor of the treatment decision. CONCLUSION: The findings of this study suggest that knowledge of the MMR status of sporadic CRC influences treatment decisions for stage II patients, in an era when clear recommendations as to how these findings should influence practice are lacking. IMPLICATIONS FOR PRACTICE: Microsatellite instability (MSI) is a molecular marker of defective DNA mismatch repair found in 15% of sporadic colorectal cancers. Until recently, expert guidelines on the role of MSI as a valid biomarker in the selection of stage II patients for adjuvant chemotherapy were lacking. Conducted at a time when the clinical utility of routine MSI testing was unclear, this study found that clinicians were influenced by MSI status in selecting stage II patients for chemotherapy. Furthermore, the impact of MSI on treatment decisions was greatest in younger patients and declined progressively until age 80 years, when no effect was found.