Trends in breast cancer incidence in Ho Chi Minh City 1996–2015: A registry-based study

The burden of breast cancer in Vietnam has not been documented. This study sought to estimate the incidence of breast cancer in Ho Chi Minh City, the largest economic center of Vietnam, from 1996 to 2015. This was a population-based study using the Ho Chi Minh City Cancer Registry as a source of data (coverage period: 1996–2015). The Registry adopted the International Classification of Diseases for Oncology, 3rd Edition for the classification of primary sites and morphology, and guidelines from the International Agency for Research on Cancer and the International Association of Cancer Registries. Using the population statistics from census data of Ho Chi Minh City, the point incidence of breast cancer for 5-year period was estimated. Based on the national population, we calculated the age-standardized rate (ASR) of breast cancer between 1996 and 2015. Overall 14,222 new cases of breast cancer (13,948 women, or 98%) had been registered during the 1996–2015 period; among whom, just over half (52%) were in the 2nd stage and 26% in the 3rd and 4th stages. In women, the median age at diagnosis was 50 years and there was a slight increase over time. The ASR of breast cancer during the 2011–2015 period was 107.4 cases per 100,000 women, representing an increase of 70% compared to the rate during the 1996–2000 period. In men, there was also a significant increase in the ASR: from 1.13 during the 1996–2001 period to 2.32 per 100,000 men during the 2011–2015 period. These very first data from Vietnam suggest that although the incidence of breast cancer in Vietnam remains relatively low, it has increased over time.


Introduction
Line 79-80: "Vietnam is the 15th most populous country in the world, with a population of 97 million (2020 statistics).Please Cite reference here.
Additionally, breast cancer risk factors should also be addressed in introduction.

Study design and method
This section needs to include relevant statistical methods used for data analysis.It is recommended that use median and IQR for nonparametric data (age diagnosis) and use kruskal wallis test to measure the difference among age groups of diagnosed cases in case of scale measurements and use chi-square where percentages are compared.Further, Join-point regression can be used for trend analysis.
Line 115-116 "we computed the point incidence of breast cancer for each 5-year period… 2010, and 2011 -2015 inclusive".Briefly, mention how that incidence rate was calculated?Line 118-119: "we calculated the age-standardized incidence rate for each of the 4 periods…" How age-standardized incidence rate was calculated?Line 119-121: "We also employed a segmented Poisson regression model to estimate the change in the incidence of breast cancer over time.All statistical analyses were conducted using the R Statistical Environment….".
It is recommended that use join-point regression technique and report your results in form of estimated annual percentage change (EAPC) with 95% UI.Please mention R version and package name that used for analysis.

Results
Line 125: findings (13,498 women, or 95%) and same in abstract, are inconsistent with results calculated in Table 1.(Table 1 has 13,948 women, 98%).Additionally report p-value of test difference and chi-square value.Line 133-138, "The average at diagnosis was 52 years (SD 11.6) and 56.3 years (13.4) for women and men, respectively.In women, there was a slight but statistically significant increase …….(Table 2)".
Firstly, data is nonparametric so authors should report median with IQR for age diagnosis, rather than mean and SD.Author reported median age in abstract but results section included mean age?Please be consistent.Authors reported that "in women statistically significant increase in the average age of diagnosis of breast cancer during 1996 and 2015….".This difference look non-significant; please report p-value with test statistic value.Also, include these results in Table .Table 2 can be revised using joint-point regression estimate (EAPC with 95%UI for each duration).Line:143-149: "Segmented regression indicated that there were two trends in the incidence of breast cancer in women: the first period occurred between ….(Figure 1).Further analysis showed that there was a statistically significant increase in the age-specific incidence of breast cancer over the period of 1996 and 2015, and the increase ….(Figure 2).In women, the increase in the age-specific incidence rate was observed among those aged…..".
Join-point regression is widely used trend analysis technique and segmented regression is a part of it.Therefore, it is suggested that use main name of the technique for convenience of the readers.
Figure 1 and 2 , are not readable.A better presentation is needed here.Author should draw the trends across ages, years and cohort by year and age group (e.g.within age Group, within year and within cohort).Through these 3 figures Table 2 results can be well representative.Line 160: Table 3. Briefly explain how the standardization was performed (ASR)?

Conclusion
Line 53-54: "These very first data from Vietnam suggest that although the incidence of breast cancer in Vietnam remains relatively low, it has increased over time, and that the increase was mainly attributable to those age groups of 50 and 70".Finally, authors concluded that "Our data also confirm that Vietnamese women tend to have breast cancer at younger ages compared to Caucasian women".Younger ages?Conclusion is not consistent with the findings.(Further, most of the GBD studies reported that women breast cancer is more prevalent in older ages worldwide).Make any changes to the abstract that align with those made in the text.

Minor comments
Line 34: Revise sentence structure (In line with the related literature, for example, see following literature)