Lawrence Paszat

University of Toronto, Toronto, Ontario, Canada

Are you Lawrence Paszat?

Claim your profile

Publications (189)1041.42 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Timely follow-up of fecal occult blood screening with colonoscopy is essential for achieving colorectal cancer mortality reduction. This study evaluates the effectiveness of two ongoing interventions designed to improve colonoscopy uptake after a positive fecal occult blood test (FOBT) result within Ontario's population-wide ColonCancerCheck program. The first was a revision of mailed FOBT lab results to physicians to explicitly define a positive FOBT and to recommend colonoscopy. The second was a letter to participants informing them of the positive FOBT and urging them to seek appropriate follow-up. Prospective cohort study using Ontario's ColonCancerCheck program data sets (2008-2011), linked to provincial administrative health databases. Crude rate ratios were calculated to assess determinants of colonoscopy uptake among an Ontario-wide FOBT-positive cohort with rolling enrolment, followed from October 2008 through February 2011. Segmented time-series regression was used to assess the average additional change in colonoscopy uptake after FOBT-positive status following the introduction of two ongoing interventions among the same cohort. A notification mailed directly to FOBT-positive screening participants was observed to increase colonoscopy uptake, beyond the modest average underlying increase throughout the study period, by an average of 3% per month (multivariable-adjusted RR: 1.03, 95% CI: 1.00-1.06). However, revision of the existing FOBT result notification to physicians was observed to have no effect. Direct participant notification of a positive FOBT result improved adherence with follow-up colonoscopy in Ontario's population-wide ColonCancerCheck program. Further participant-directed interventions may be an effective means of maximizing adherence in population-wide screening.
    Implementation Science 12/2015; 10(1):226. DOI:10.1186/s13012-015-0226-0 · 3.47 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Women with diabetes have higher breast cancer incidence and mortality. The purpose of this study was to examine the impact of diabetes on stage at breast cancer diagnosis, as a possible reason for their higher mortality. Using population-based health databases from Ontario, Canada, this retrospective cohort study examined stage at diagnosis (II, III, or IV vs I) among women aged 20-105 years who were newly diagnosed with invasive breast cancer between 2007 and 2012. We compared those with diabetes to those without diabetes. Diabetes was defined based on medical records using a validated algorithm. Among 38,407 women with breast cancer, 6115 (15.9 %) women had diabetes. Breast cancer patients with diabetes were significantly more likely to present with advanced-stage breast cancer than those without diabetes. After adjustment for mammograms and other covariates, diabetes was associated with a significantly increased risk of Stage II [adjusted odds ratio (aOR) 1.14, 95 % confidence interval (CI) 1.07, 1.22], Stage III (aOR 1.21, 95 % CI 1.11, 1.33), and Stage IV (aOR 1.16, 95 % CI 1.01, 1.33) versus Stage I breast cancer. Women with diabetes had a higher risk of lymph node metastases (aOR 1.16, 95 % CI 1.06, 1.27) and tumors with size over 2 cm (aOR 1.16, 95 % CI 1.06, 1.28). Diabetes was associated with more advanced-stage breast cancer, even after accounting for differences in screening mammogram use and other factors. Our findings suggest that diabetes may predispose to more aggressive breast cancer, which may be a contributor to their higher cancer mortality.
    Breast Cancer Research and Treatment 03/2015; DOI:10.1007/s10549-015-3323-5 · 4.20 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A clinical risk index that uses distal colorectal findings at flexible sigmoidoscopy (FS) in conjunction with easily determined risk factors for advanced proximal neoplasia (APN) may be useful for tailoring or prioritizing screening with colonoscopy. To conduct an external evaluation of a previously published risk index in a large, well-characterized cohort. Cross-sectional. Teaching hospital and colorectal cancer screening center. A total of 5139 asymptomatic persons aged 50 to 74 (54.9% women) with a mean age (± SD) of 58.3 (± 6.2) years. Between 2003 and 2011, all participants underwent a complete screening colonoscopy and removal of all polyps. Participants were classified as low, intermediate, or high risk for APN, based on their composite risk index scores. The concordance or c-statistic was used to measure discriminating ability of the risk index. A total of 167 persons (3.2%) had APN. The prevalence of those with APN among low-, intermediate-, and high-risk categories was 2.1%, 2.9%, and 6.5%, respectively. High-risk individuals were 3.2 times more likely to have APN compared with those in the low-risk category. The index did not discriminate well between those in the low- and intermediate-risk categories. The c-statistic for the overall index was 0.62 (95% confidence interval, 0.58-0.66). Distal colorectal findings were derived from colonoscopies and not FS itself. The risk index discriminated between those at low risk and those at high risk, but it had limited ability to discriminate between low- and intermediate-risk categories for prevalent APN. Information on other risk factors may be needed to tailor, or prioritize, access to screening colonoscopy. Copyright © 2015 American Society for Gastrointestinal Endoscopy. Published by Elsevier Inc. All rights reserved.
  • [Show abstract] [Hide abstract]
    ABSTRACT: The potential for cancers to not be detected on colonoscopy is increasingly recognised, but little is known about patient outcomes. The objective of this study was to assess the outcomes of patients diagnosed with postcolonoscopy colorectal cancers (PCCRCs). We conducted a population-based retrospective cohort study, including all patients diagnosed with colorectal cancer (CRC) in Ontario, Canada from 2003 to 2009. Patients were categorised into three groups: DETECTED (diagnosed within 6 months of first colonoscopy), PCCRC (diagnosed 6-36 months after first colonoscopy) or NOSCOPE (no colonoscopy within 36 months of diagnosis). Univariate and multivariable analyses were conducted to study overall survival, surgical treatment, emergency presentation and surgical complications. Overall, 45 104 patients were included, with 2804 being classified as having a PCCRC. Compared with the DETECTED group, PCCRC was associated with a significantly higher likelihood of stage IV disease (17.2% vs 12.9%), worse overall survival (5 year OS: 60.8% vs 68.3%, p<0.0001; adjusted HR: 1.25, 95% CI 1.17 to 1.32, p<0.0001), a higher likelihood of emergency presentation (OR: 2.86, 95% CI 2.56 to 3.13, p<0.001) and lower likelihood of surgical resection (OR: 0.61, 95% CI 0.55 to 0.67, p<0.001). However, patients with PCCRC had significantly better outcomes than those in the NOSCOPE group (stage IV: 37.1%, 5 year OS: 38.9%) CONCLUSIONS: Compared with CRC detected by colonoscopy, PCCRCs are associated with a higher risk of emergent presentation, a lower likelihood of surgical resection and most notably, significantly worse oncological outcomes. However, they have better outcomes than patients with no recent colonoscopy. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to
    Gut 03/2015; DOI:10.1136/gutjnl-2014-308578 · 13.32 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In the province-wide colorectal cancer (CRC) screening program in Ontario, Canada, individuals with a family history of CRC are offered colonoscopy screening and those without are offered guaiac fecal occult blood testing (gFOBT, Hemoccult II). We used microsimulation modeling to estimate the cumulative number of CRC deaths prevented and colonoscopies performed between 2008 and 2038 with this family history-based screening program, compared to a regular gFOBT program. In both programs, we assumed screening uptake increased from 30% (participation level in 2008 before the program was launched) to 60%. We assumed that 11% of the population had a family history, defined as having at least one first-degree relative diagnosed with CRC. The programs offered screening between age 50-74 years, every two years for gFOBT, and every ten years for colonoscopy. Compared to opportunistic screening (2008 participation level kept constant at 30%), the gFOBT program cumulatively prevented 6,700 more CRC deaths and required 570,000 additional colonoscopies by 2038. The family history-based screening program increased these numbers to 9,300 and 1,100,000, a 40% and 93% increase, respectively. If biennial gFOBT was replaced with biennial fecal immunochemical test (FIT), annual Hemoccult Sensa or five-yearly sigmoidoscopy screening, both the added benefits and colonoscopies required would decrease. A biennial gFOBT screening program that identifies individuals with a family history of CRC and recommends them to undergo colonoscopy screening would prevent 40% (range in sensitivity analyses: 20-51%) additional deaths while requiring 93% (range: 43-116%) additional colonoscopies, compared to a regular gFOBT screening program. This article is protected by copyright. All rights reserved. © 2014 Wiley Periodicals, Inc. © 2015 UICC.
    International Journal of Cancer 02/2015; DOI:10.1002/ijc.29473 · 5.01 Impact Factor
  • JAMA The Journal of the American Medical Association 12/2014; 312(21):2285-6. DOI:10.1001/jama.2014.14038 · 30.39 Impact Factor
  • Rachel Kupets, Yan Lu, Danielle Vicus, Lawrence Paszat
    [Show abstract] [Hide abstract]
    ABSTRACT: Objective: To define the patterns of care of women after they have been referred to a colposcopic service. Methods: We carried out this population-based study by linking databases of health care provision for 2010. We defined "colposcopic episodes of care" as a series of colposcopic evaluations beginning at the time of referral for colposcopy because of a new cervical cytology abnormality and continuing until no colposcopy or cytology service had been performed for ≥ 365 days. Results: Cytology reports indicating low-grade squamous intraepithelial lesions and atypical squamous cells of uncertain significance account for 88% of referrals of women for colposcopy. Women aged 20 to 29 had the highest rates of referral and treatments. Up to 87% of women referred for low-grade squamous intraepithelial lesions cytology did not require treatment after colposcopic evaluation, while 54% of women referred for high-grade squamous intraepithelial lesions cytology required treatment. The duration of colposcopic episodes of care in which treatment was carried out lasted up to 327 days, with a median three colposcopic evaluations per episode, whereas episodes of care in which no treatment was carried out lasted up to 190 days with a median of one or two colposcopic examinations per episode. Conclusion: Young women aged 20 to 29 have the highest rates of colposcopic services. Women referred because of cytology showing high-grade squamous intraepithelial lesions in whom treatment is not carried out require more extensive follow-up to ensure that lesions are not missed. We recommend the incorporation of colposcopy services into centralized cervical cancer screening programs.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Background:Prior randomized, controlled trials (RCTs) indicate patient navigation can boost colorectal cancer (CRC) screening in primary care. The sparse literature on pragmatic trials of interventions designed to increase CRC screening adherence motivated this trial on the impact of a patient navigation intervention that included support for performance of the participants' preferred screening test (colonoscopy or stool blood testing). Methods:Primary-care patients (n = 5240), 50-74 years of age, with no prior diagnosis of bowel cancer, and no record of a recent CRC screening test were identified at the Group Health Centre in northern Ontario. These patients were randomly assigned to an Intervention Group (N = 2629) or a usual care Control Group (N = 2611). Intervention Group participants were contacted by a trained nurse navigator by telephone to discuss CRC screening. Interested patients met with the navigator, who helped them identify and arrange for performance of the preferred screening test. Multivariate analyses were conducted using medical records data to assess intervention impact on screening adherence within 12 months after randomization. Results: Mean patient age was 59 years, and 50% of participants were women. CRC screening adherence was higher in the Intervention Group (35%) compared to the Control Group (20%), a difference that was statistically significant (OR-2.11, CI: 1.87 - 2.39). Conclusions: Preference-based patient navigation increased screening uptake in a pragmatic RCT. Impact: Patient navigation increased CRC screening rates in a pragmatic RCT in proportions similar to those observed in explanatory RCTs.
    Cancer Epidemiology Biomarkers & Prevention 11/2014; DOI:10.1158/1055-9965.EPI-14-0744 · 4.32 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Objective: The aim of this study was to estimate the effect of cervical screening in the prevention of invasive cervical cancer among age groups, using a population-based case-control study in the province of Ontario, Canada. Methods: Exposure was defined as cervical cytology history greater than 3 months before the diagnosis date of cervical cancer (index date). Cases were women who were diagnosed with cervical cancer between January 1, 1998, and December 31, 2008. Controls were women without a diagnosis of cervical cancer on, or before, December 31, 2008. Two controls were matched to each case on year of birth and income quintile, as of the index date. Conditional logistic regression was used to estimate the odds ratio for having been screened among those with cervical cancer. Results: Cervical cancer screening performed between 3 and 36 months before the index date was protective against invasive cervical cancer in women aged 40 through 69 years. In women younger than 40 years, cervical cancer screening performed 3 to 36 months before the index date was not protective. Conclusions: Cervical screening is associated with a reduced risk for invasive cervical cancer among women older than 40 years. Cervical cancer resources should be focused on maximizing the risk reduction.
    International Journal of Gynecological Cancer 11/2014; 25(1). DOI:10.1097/IGC.0000000000000305 · 1.95 Impact Factor
  • Rachel Kupets, Yan Lu, Danielle Vicus, Lawrence Paszat
    [Show abstract] [Hide abstract]
    ABSTRACT: Background: When cervical cytology screening shows atypical squamous cells of unknown significance (ASCUS) or low-grade squamous intraepithelial lesion (LSIL), and cervical cytology screening has not been performed in the previous year, it is recommended that cytology screening be repeated six months later. Women with persistent abnormalities should be referred for colposcopy. We explored provincial databases in Ontario to determine whether these recommendations were always followed. Methods: Cervical cytology reports in Ontario are contained in a provincial database, deterministically linkable to other health services databases, including those recording physician reimbursement claims for colposcopy. We identified all women in Ontario who had a first time diagnosis of ASCUS or LSIL in 2008 or 2009. We searched for additional cytology reports and for colposcopy billing claims during the 24 months following the date of the first abnormal report. We assessed the interaction of socioeconomic status, having abnormal cytology, and having repeat cytology after a report of low-grade abnormal cervical cytology. Results: A total of 74 770 women had a first time report of low-grade abnormal cytology. Among women with ASCUS and LSIL, 69.7% and 60.3%, respectively, underwent repeat cytology. Repeat cytology following ASCUS disclosed normal (68.2%), ASCUS (19.3%), LSIL (10.6%), and high-grade squamous intraepithelial lesion (1.4%); following LSIL, the corresponding percentages were 48.3%, 18.0%, 30.8%, and 2.6%. Of women with ASCUS, 16.2% went directly for colposcopy; 14.0% did not repeat cytology or go for colposcopy. Of women with LSIL, 26.4% went directly for colposcopy but 13.4% had no follow-up. Conclusion: We have demonstrated the potential for substantial improvement in cervical cytology six months after a finding of ASCUS and LSIL. We found that many women with ASCUS and LSIL had unnecessary referrals directly for colposcopy, and we identified a lack of follow-up for one sixth of women with low-grade abnormal cytology.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Regular screening using guaiac fecal occult blood test (gFOBT) reduces mortality from colorectal cancer (CRC). The objective of this study was to determine whether the addition of a gFOBT kit to a 2nd mailed invitation compared to a 2nd mailed invitation alone increases CRC screening among eligible persons who did not respond to an initial mailed invitation. We conducted a cluster randomized controlled trial, with the physician as the unit of randomization. Participants were persons who had been invited but who had not responded to an invitation for CRC screening in an earlier pilot project. The intervention group received a mailed gFOBT kit and 2nd mailed CRC screening invitation (n=2008) while the control group received a 2nd mailed CRC screening invitation alone (n=1586). The primary outcome was the uptake of gFOBT within 6 months of the 2nd mailing. We found that the uptake of gFOBT was more than twice as high in the intervention group (20.1%) compared to the control group (9.6%). The absolute difference between the 2 groups was 10.5% (95% CI: 7.5 – 13.4%, p=<0.0001). In a subsequent adjusted analysis, participants in the intervention group were twice as likely to complete the test as those in the control group (OR=2.1; 95% CI: 1.6-2.6). These findings suggest that directly mailed gFOBT kits increases CRC screening participation among previous non-responders to a mailed invitation and that approximately 10 gFOBT kits would have to be sent by mail in order to screen 1 additional person. ( NCT01629004). © 2014 Wiley Periodicals, Inc.
    International Journal of Cancer 09/2014; 136(6). DOI:10.1002/ijc.29191 · 5.01 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Purpose Whole-breast radiation therapy (XRT) after breast-conserving surgery (BCS) for ductal carcinoma in situ (DCIS) may decrease the risk of local recurrence, but the optimal dose regimen remains unclear. Past studies administered 50 Gy in 25 fractions (conventional); however, treatment pattern studies report that hypofractionated (HF) regimens (42.4 Gy in 16 fractions) are frequently used. We report the impact of HF (vs conventional) on the risk of local recurrence after BCS for DCIS. Methods and Materials All women with DCIS treated with BCS and XRT in Ontario, Canada from 1994 to 2003 were identified. Treatment and outcomes were assessed through administrative databases and validated by chart review. Survival analyses were performed. To account for systematic differences between women treated with alternate regimens, we used a propensity score adjustment approach. Results We identified 1609 women, of whom 971 (60%) received conventional regimens and 638 (40%) received HF. A total of 489 patients (30%) received a boost dose, of whom 143 (15%) received conventional radiation therapy and 346 (54%) received HF. The median follow-up time was 9.2 years. The median age at diagnosis was 56 years (interquartile range [IQR], 49-65 years). On univariate analyses, the 10-year actuarial local recurrence–free survival was 86% for conventional radiation therapy and 89% for HF (P=.03). On multivariable analyses, age <45 years (hazard ratio [HR] = 2.4; 95% CI: 1.6-3.4; P<.0001), high (HR=2.9; 95% CI: 1.2-7.3; P=.02) or intermediate nuclear grade (HR=2.7; 95% CI: 1.1-6.6; P=.04), and positive resection margins (HR=1.4; 95% CI: 1.0-2.1; P=.05) were associated with an increased risk of local recurrence. HF was not significantly associated with an increased risk of local recurrence compared with conventional radiation therapy on multivariate analysis (HR=0.8; 95% CI: 0.5-1.2; P=.34). Conclusions The risk of local recurrence among individuals treated with HF regimens after BCS for DCIS was similar to that among individuals treated with conventional radiation therapy.
    International journal of radiation oncology, biology, physics 09/2014; DOI:10.1016/j.ijrobp.2014.07.026 · 4.18 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Since the publication of two randomized controlled trials (RCT) in 1996 demonstrating the effectiveness of fecal occult blood test (FOBT) in reducing colorectal cancer (CRC) mortality, several public health initiatives have been introduced in Ontario to promote FOBT participation. We examined the effect of these initiatives on FOBT participation and evaluated temporal trends in participation between 1994 and 2012.
    BMC Cancer 07/2014; 14(1):537. DOI:10.1186/1471-2407-14-537 · 3.32 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: OBJECTIVES:The sessile serrated adenoma/polyp (SSA/P) is increasingly recognized as an important precursor to colorectal cancer (CRC) and may contribute to proximal postcolonoscopy CRCs. Hyperplastic polyps (HPs) generally follow a more benign course than do SSA/Ps, but they have a similar histologic appearance. Our aims were to identify patient and polyp factors associated with reclassification of HPs as SSA/Ps during a central pathology review and to characterize and compare their subsequent clinical management with other polyps.METHODS:From 2003 to 2008, we prospectively enrolled asymptomatic persons aged 50-74 years in a study of screening colonoscopy. Because criteria for SSA/P diagnosis evolved over our study period, we initiated a second review of all HPs >5 mm in size in 2011, with reclassification of polyps if indicated. Rates of subsequent colonoscopies, polypectomies, and CRCs were identified.RESULTS:We enrolled 2,527 persons who underwent colonoscopy in whom 111 had HPs >5 mm. Thirty-two of the 111 participants (28.8%) with HPs >5 mm had their polyps reclassified as SSA/Ps. There were no significant differences in patient characteristics between those with reclassified SSA/Ps and those who had HPs >5 mm. SSA/Ps were more likely to be proximal (P<0.001) and larger (P<0.007) than the HPs. In all, 48.3% of those with high-risk adenomas received appropriate follow-up compared with 26.1% of those with high-risk SSA/Ps.CONCLUSIONS:Almost 1/3 of recently diagnosed HPs >5 mm were reclassified as SSA/Ps. Patients previously diagnosed with larger HPs in the proximal colon may benefit from a pathologic review to ensure appropriate diagnosis and follow-up.Am J Gastroenterol advance online publication, 8 July 2014; doi:10.1038/ajg.2014.78.
    The American Journal of Gastroenterology 07/2014; 109(11). DOI:10.1038/ajg.2014.78 · 9.21 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: PURPOSE There is limited evidence for the effectiveness of pay for performance despite its widespread use. We assessed whether the introduction of a pay-for-performance scheme for primary care physicians in Ontario, Canada, was associated with increased cancer screening rates and determined the amounts paid to physicians as part of the program. METHODS We performed a longitudinal analysis using administrative data to determine cancer screening rates and incentive costs in each fiscal year from 1999/2000 to 2009/2010. We used a segmented linear regression analysis to assess whether there was a step change or change in screening rate trends after incentives were introduced in 2006/2007. We included all Ontarians eligible for cervical, breast, and colorectal cancer screening. RESULTS We found no significant step change in the screening rate for any of the 3 cancers the year after incentives were introduced. Colon cancer screening was increasing at a rate of 3.0% (95% CI, 2.3% to 3.7%) per year before the incentives were introduced and 4.7% (95% CI, 3.7% to 5.7%) per year after. The cervical and breast cancer screening rates did not change significantly from year to year before or after the incentives were introduced. Between 2006/2007 and 2009/2010, $28.3 million, $31.3 million, and $50.0 million were spent on financial incentives for cervical, breast, and colorectal cancer screening, respectively. CONCLUSIONS The pay-for-performance scheme was associated with little or no improvement in screening rates despite substantial expenditure. Policy makers should consider other strategies for improving rates of cancer screening.
    The Annals of Family Medicine 07/2014; 12(4):317-23. DOI:10.1370/afm.1664 · 4.57 Impact Factor
  • R. Kupets, L. Paszat
    Gynecologic Oncology 06/2014; 133:151. DOI:10.1016/j.ygyno.2014.03.396 · 3.69 Impact Factor
  • Gastroenterology 05/2014; 146(5):S-404. DOI:10.1016/S0016-5085(14)61462-1 · 13.93 Impact Factor
  • Gastroenterology 05/2014; 146(5):S-32-S-33. DOI:10.1016/S0016-5085(14)60113-X · 13.93 Impact Factor
  • Gastroenterology 05/2014; 146(5):S-176. DOI:10.1016/S0016-5085(14)60622-3 · 13.93 Impact Factor

Publication Stats

5k Citations
1,041.42 Total Impact Points


  • 2000–2015
    • University of Toronto
      • • Institute of Health Policy, Management and Evaluation
      • • Institute for Clinical Evaluative Sciences
      • • Department of Surgery
      • • Department of Medicine
      • • Department of Radiation Oncology
      Toronto, Ontario, Canada
    • Kingston General Hospital
      Kingston, Ontario, Canada
  • 2004–2014
    • Sunnybrook Health Sciences Centre
      • • Department of Radiation Oncology
      • • Department of Medicine
      • • Department of Evaluative Clinical Sciences
      • • Division of Medical Oncology and Hematology
      Toronto, Ontario, Canada
  • 2003–2014
    • Institute for Clinical Evaluative Sciences
      Toronto, Ontario, Canada
  • 2007–2013
    • Women's College Hospital
      Toronto, Ontario, Canada
    • University of Texas MD Anderson Cancer Center
      • Department of Gynecologic Oncology
      Houston, TX, United States
    • Dalhousie University
      Halifax, Nova Scotia, Canada
    • McMaster University
      • Department of Obstetrics and Gynaecology
      Hamilton, Ontario, Canada
  • 2012
    • University Health Network
      • Division of Gynecologic Oncology
      Toronto, Ontario, Canada
  • 2009
    • University of British Columbia - Vancouver
      • Division of Gynaecologic Oncology
      Vancouver, British Columbia, Canada
  • 1998–2003
    • Cancer Care Ontario
      Toronto, Ontario, Canada
  • 1997–2001
    • Queen's University
      • Department of Oncology
      Kingston, Ontario, Canada