Title: INCIDENCE AND RISK FACTORS FOR COLORECTAL CANCER IN AFRICA: A
SYSTEMATIC REVIEW AND META-ANALYSIS
Version: 0 Date: 07 Dec 2023
Reviewer's report:
Thank you for the opportunity to review the manuscript entitled “Incidence and risk factors for
colorectal cancer in Africa: A systematic review and meta-analysis”.
The authors sought to evaluate risk factors for colorectal cancer in Africa and to quantify the
incidence rate for colorectal cancer in Africa.
I have several concerns about the validity of the study design, as well as the validity of some
of the assumptions made by the authors:
1. The pooled incidence rate for colorectal cancer (CRC) in Africa is not scientifically
informative. Cancer incidences are reported by country (where possible) or extrapolated using
neighbouring country’s data in the absence of source data within a given country. The pooling of
published CRC incidence has a strong publication bias and it is not informative for continental
Africa. Secondly, African CRC incidence rates are published by the African Cancer Registry
Network and through the International Agency for Research on Cancer (Globocan). It would be
unwise to publish incidence rates without taking into consideration the Globocan data.
2. Regarding the pool incidence rate. At best, the authors can claim that it is the pooled
CRC incidence rate based on publications from Egypt, South Africa, Tunisia, Morocco
and Zimbabwe. However, pooling incidence rates the assumption that the populations are
homogeneous. This assumption is not met. The heterogeneous nature of African populations in
terms of genetics and environmental exposures is vast. Northern Africa and sub-Saharan Africa
can not be grouped together for analysis of this nature. Additionally, South Africa and Zimbabwe
are not representative of sub-Saharan Africa.
3. In terms of statistical methodology, odds ratios and relative risk are not the same measure and
often can not be directly equated.
4. Perhaps would be a better approach to perform the meta-analysis on studies from North
Africa to quantify the pooled incidence rates and then compare the incidence rates reported on
Globocan. Thereafter, meta-analyse the risk factors and report on its findings. However, as it
stands, the findings in this manuscript are misleading. The source data are not representative
and the methodologies are flawed.
Title: INCIDENCE AND RISK FACTORS FOR COLORECTAL CANCER IN AFRICA: A
SYSTEMATIC REVIEW AND META-ANALYSIS
Version: 0 Date: 07 Dec 2023
Reviewer's report:
Thank you for the opportunity to review the manuscript entitled “Incidence and risk factors for
colorectal cancer in Africa: A systematic review and meta-analysis”.
The authors sought to evaluate risk factors for colorectal cancer in Africa and to quantify the
incidence rate for colorectal cancer in Africa.
I have several concerns about the validity of the study design, as well as the validity of some
of the assumptions made by the authors:
1. The pooled incidence rate for colorectal cancer (CRC) in Africa is not scientifically
informative. Cancer incidences are reported by country (where possible) or extrapolated using
neighbouring country’s data in the absence of source data within a given country. The pooling of
published CRC incidence has a strong publication bias and it is not informative for continental
Africa. Secondly, African CRC incidence rates are published by the African Cancer Registry
Network and through the International Agency for Research on Cancer (Globocan). It would be
unwise to publish incidence rates without taking into consideration the Globocan data.
2. Regarding the pool incidence rate. At best, the authors can claim that it is the pooled
CRC incidence rate based on publications from Egypt, South Africa, Tunisia, Morocco
and Zimbabwe. However, pooling incidence rates the assumption that the populations are
homogeneous. This assumption is not met. The heterogeneous nature of African populations in
terms of genetics and environmental exposures is vast. Northern Africa and sub-Saharan Africa
can not be grouped together for analysis of this nature. Additionally, South Africa and Zimbabwe
are not representative of sub-Saharan Africa.
3. In terms of statistical methodology, odds ratios and relative risk are not the same measure and
often can not be directly equated.
4. Perhaps would be a better approach to perform the meta-analysis on studies from North
Africa to quantify the pooled incidence rates and then compare the incidence rates reported on
Globocan. Thereafter, meta-analyse the risk factors and report on its findings. However, as it
stands, the findings in this manuscript are misleading. The source data are not representative
and the methodologies are flawed.
Please review this paper.
user
Title: INCIDENCE AND RISK FACTORS FOR COLORECTAL CANCER IN AFRICA: A
SYSTEMATIC REVIEW AND META-ANALYSIS
Version: 0 Date: 07 Dec 2023
Reviewer's report:
Thank you for the opportunity to review the manuscript entitled “Incidence and risk factors for
colorectal cancer in Africa: A systematic review and meta-analysis”.
The authors sought to evaluate risk factors for colorectal cancer in Africa and to quantify the
incidence rate for colorectal cancer in Africa.
I have several concerns about the validity of the study design, as well as the validity of some
of the assumptions made by the authors:
1. The pooled incidence rate for colorectal cancer (CRC) in Africa is not scientifically
informative. Cancer incidences are reported by country (where possible) or extrapolated using
neighbouring country’s data in the absence of source data within a given country. The pooling of
published CRC incidence has a strong publication bias and it is not informative for continental
Africa. Secondly, African CRC incidence rates are published by the African Cancer Registry
Network and through the International Agency for Research on Cancer (Globocan). It would be
unwise to publish incidence rates without taking into consideration the Globocan data.
2. Regarding the pool incidence rate. At best, the authors can claim that it is the pooled
CRC incidence rate based on publications from Egypt, South Africa, Tunisia, Morocco
and Zimbabwe. However, pooling incidence rates the assumption that the populations are
homogeneous. This assumption is not met. The heterogeneous nature of African populations in
terms of genetics and environmental exposures is vast. Northern Africa and sub-Saharan Africa
can not be grouped together for analysis of this nature. Additionally, South Africa and Zimbabwe
are not representative of sub-Saharan Africa.
3. In terms of statistical methodology, odds ratios and relative risk are not the same measure and
often can not be directly equated.
4. Perhaps would be a better approach to perform the meta-analysis on studies from North
Africa to quantify the pooled incidence rates and then compare the incidence rates reported on
Globocan. Thereafter, meta-analyse the risk factors and report on its findings. However, as it
stands, the findings in this manuscript are misleading. The source data are not representative
and the methodologies are flawed.
assistant