Review for 10.1186/s12876-021-01823-4 (2021)

Reviewer’s report
Title: 
Simultaneous gastric cancer and breast cancer metastases to the stomach
with lymph node collision tumor: a case report
Version: 
0 
Date: 
01 Apr 2021
Reviewer's report:
In this case report, the authors presented a 51 y/o woman with a 3-year history of
breast cancer (invasive ductal carcinoma, ER [+], PR [+], Her-2 [-], with
extensive bony metastasis) s/p leuprorelin, tamoxifen, denosumab, and
paclitaxel. She then suffered from melena and was diagnosed as simultaneous
advanced gastric cancer involving pylorus and metastatic breast cancer involving
whole stomach. She received distal gastrectomy and one resected lymph node
had evidence of both stomach cancer and breast cancer metastases, forming a
collision tumor. 
This case report is quite unique and educative. There is only one similar report of
simultaneous presence of primary gastric cancer and metastatic breast cancer in
stomach. The IHC of the resected specimens in this patient also provided strong
evidence of the diagnosis. The manuscript adheres well to the CARE checklist
for case reports.
There is one point that I would like to address:
1. In the Background section of the Abstract, the authors wrote "While double
primary cancers are becoming more common, two cancers arising simultaneously
in the same organ are exceedingly rare." It's somewhat inaccurate as we know
that it's uncommon but not rare to find primary gastric cancer and gastric
MALToma. It's also not rare to find HCC and metastatic colon cancer in liver. I
would suggest the authors to change this statement to fit more to the case they
reported. For example, the authors may say "While double primary cancers are
common in breast cancer patients, co-existence of primary gastric cancer and
gastric metastases of breast cancer is exceedingly rare".
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