On 2015 Feb 24, Amanda Capes-Davis commented:

Are the authors able to comment further on the cell lines used in this study, to confirm that results are not related to the cell culture models used?

The Materials and Methods section states that cell lines (MCF-7, MCF-10A and BT549) were obtained from the ATCC and authenticated before purchase. I am very pleased to see information included on source and previous testing. However, it is not clear how long ago testing was performed. In some cases, cell lines are used by many different laboratory members and may be passed from laboratory to laboratory. That gives time for cross-contamination or other cell culture problems to arise. Mycoplasma contamination, or cross-contamination by another cell line, might result in behavioral changes at the time that morphine is introduced.

The results here have significant clinical implications, suggesting that pain control in breast cancer may contribute to chemoresistance. So it is essential to ensure that cell culture models are tested to eliminate any possibility of artefacts.

I particularly raise this issue because, as the authors note in their Discussion, previous studies have suggested that morphine decreases cell proliferation in many cancer cell types.

The International Cell Line Authentication Committee (ICLAC) has released a checklist that sets out cell line reporting requirements for manuscripts and grant applications. The checklist can be found at http://iclac.org/resources/cell-line-checklist/.

On 2015 Feb 24, Amanda Capes-Davis commented:

Are the authors able to comment further on the cell lines used in this study, to confirm that results are not related to the cell culture models used?

The Materials and Methods section states that cell lines (MCF-7, MCF-10A and BT549) were obtained from the ATCC and authenticated before purchase. I am very pleased to see information included on source and previous testing. However, it is not clear how long ago testing was performed. In some cases, cell lines are used by many different laboratory members and may be passed from laboratory to laboratory. That gives time for cross-contamination or other cell culture problems to arise. Mycoplasma contamination, or cross-contamination by another cell line, might result in behavioral changes at the time that morphine is introduced.

The results here have significant clinical implications, suggesting that pain control in breast cancer may contribute to chemoresistance. So it is essential to ensure that cell culture models are tested to eliminate any possibility of artefacts.

I particularly raise this issue because, as the authors note in their Discussion, previous studies have suggested that morphine decreases cell proliferation in many cancer cell types.

The International Cell Line Authentication Committee (ICLAC) has released a checklist that sets out cell line reporting requirements for manuscripts and grant applications. The checklist can be found at http://iclac.org/resources/cell-line-checklist/.