Comments on abstract, title, references ● Is the aim clear? Yes ● Is it clear what the study found and how they did it? Yes ● Is the title informative and relevant? Yes ● Are the references: ● Relevant? Yes ● Recent? Yes ● Referenced correctly? Yes ● Are appropriate key studies included? Yes

Comments on introduction/background ● Is it clear what is already known about this topic? Yes ● Is the research question clearly outlined? Yes ● Is the research question justified given what is already known about the topic? Yes but I think that the comparison between the performance of screening and diagnostic mammography is not that meaningful question. It will not add a new knowledge in any setting.

Comments on methodology ● Is the process of subject selection clear? Yes ● Are the variables defined and measured appropriately? Yes ● Are the study methods valid and reliable? Yes ● Is there enough detail in order to replicate the study? Please provide additional information about the target population for the study. Have women underwent basal mammograms or subsequent mammograms

Comments on data and results ● Is the data presented in an appropriate way? Yes ● Tables and figures relevant and clearly presented? Yes ● Appropriate units, rounding, and number of decimals? Yes ● Titles, columns, and rows labelled correctly and clearly? Yes ● Categories grouped appropriately? Yes ● Does the text in the results add to the data or is it repetitive? Yes ● Are you clear about what is a statistically significant result? Yes ● Are you clear about what is a practically meaningful result? Yes.

Comments on discussion and conclusions ● Are the results discussed from multiple angles and placed into context without being over interpreted? Yes ● Do the conclusions answer the aims of the study? Yes ● Are the conclusions supported by references or results? Yes ● Are the limitations of the study fatal or are they opportunities to inform future research? They are opportunities to inform future research. ● Was the study design appropriate to answer the aim? Prospective study is more appropriate than retrospective.
● What did this study add to what was already known on this topic? The short-term outcome of opportunistic screening mammography for women in a low-income country like Malaysia. ● What were the major flaws of this article? This paper reports retrospectively on the performance of an opportunistic screening mammography which is important as a preliminary evaluation of the screening quality, but the effectiveness of screening is mainly related to the long-term outcome (mortality reduction), so we cannot conclude that screening is effective in this study without follow up which needs a cohort prospective study. Selection bias is a given limitation of an opportunistic screening due to the lack of individual invitation which is related to the fact that women with more health awareness are more likely to have the screening opportunity and this require proper approach in the discussion. ● Is the article consistent within itself? Yes

Overall statement or summary of the article and its findings in your own words The authors have retrospectively collected data for the outcome of 2510 Mammograms performed between Jan-Dec 2010. Of 2510 mammograms, 2178 mammograms were performed for asymptomatic women (screening mammography) while 332 mammograms were diagnostic mammography. In the latter group, 20 were excluded from the analysis leaving 312 cases. Of 2178 women screened, 1938 of women were at an average risk of developing breast cancer (opportunistic screening group), while 240 of them were at higher risk of developing breast cancer (targeted screening group). The authors compared the performance between three groups (opportunistic screening, targeted screening and diagnostic mammography), and then they compared the screening performance according to age categories (less than 50 years old and 50 years and above). Cancer detection rate was 5.2 per 1000 in the opportunistic screening group and 12.5 per 1000 in the targeted screening group against 260 per 1000 in the diagnostic group With regard to age categories, cancer detection rate was 2 per 1000 in women screened under 50 years of age compared to 6.2 per 1000 in women screened 50 years of age and older. The performance indicators of screening mammography were more feasible for the targeted screening group and for the older age group in terms of cancer detection rate, biopsy rate and Positive Predictive value (PPV) for biopsies. Despite the significant difference between the screening and diagnostic groups in the rate of early stage cancer, there is no difference in the mastectomy rate. The authors concluded targeted screening for women at higher risk of developing breast cancer will give a higher yield in low resources setting, and that population-based screening for all women commencing at age of 50 years and older is effective in Malaysia once resources become more available.

Overall strengths of the article and what impact it might have in your field I appreciate authors' efforts to evaluate the opportunistic screening performance in a developing country. Screening quality assessment is valuable to guide a population-based screening program that can be implemented in the future once more resources are available.

Specific comments on weaknesses of the article and what could be done to improve it Major points in the article which needs clarification, refinement, reanalysis, rewrites and/or additional information and suggestions for what could be done to improve the article.

1. The study design does not seem appropriate for the aim of study. Prospective cohort study is recommended to report on the subsequent mammograms as a follow up of the baseline mammogram.
2. Study results that determine an acceptable screening performance(short-term outcomes) do not justify drawing a conclusion that the screening is effective because the effectiveness of the screening is mainly linked to the long-term outcomes (mortality reduction)
3. Selection bias is a given limitation of an opportunistic screening and this has to be taken into account in the discussion.