1. Hi Dr Byers, I thought the recent studies showed that pre-treatment with prednisolone did NOT create a drug resistenc ein lymphoma? Maybe that is just cats? I’ll hunt around for the reference if you haven’t read that particular one. It makes sense that cancer cells can be selectively resistent in the same way as bacteria. However, while appreciating how difficult it is for the specialists, the primary care veterinarian is under somewhat different pressures – I would like to know how many ex-lap biopsies have to be done for pets-of-a-specified-group in order to find one or two cases where the differential mattered over a 12 – 18 month period. I don’t think anyone knows, which is why it is hard to sound convincing to an owner when recommending – essentially – major surgery on a .. gut .. feeling. Biology is tricky isn’t it?

    • Indeed biology can be truly tricky!

      Pre-chemotherapy glucocorticoid exposure is thought to affect response duration with minimal-to-no effect on response rate. The story about pretreatment with corticosteroids having negative impact on median survival for canine multicentric lymphoma started more than 20 years ago (Price et al, J Vet Intern Med, 1991) and has been evaluated several times since in retrospective studies. There was a recent retrospective of feline gastric LSA (Gustafson et al, J Am Anim Hosp Assoc, 2013) that showed prior treatment with prednisolone was not a significant prognostic variable. But another study by Taylor et al (J Sm Anim Pract, 2009) retrospectively evaluated feline extra nodal lymphoma. For cats in this study who achieved complete remission, prior treatment with corticosteroids significantly reduced survival time.

      Nevertheless this issue still hasn’t been rigorously studied in an organized, prospective fashion. We still don’t know the impact of different corticosteroids, different dosing regimens, different lengths of treatment before starting chemo, etc. Although the negative effects of pre-chemotherapy steroids may occur as soon as a few days after commencing use, clinically it seems like the window may be something closer to 2 weeks (at least in dogs). Until we have more data, I agree wholeheartedly with medical oncologists who state it is prudent to avoid corticosteroid pretreatment. Having said that, I recognize there are times when it is unavoidable. If you find yourself in that situation, try not to worry about it…too much! A major point is to avoid starting steroids before staging is complete.

      To your second point as to whether the differential matters (and if I interpreted your point correctly), I wholeheartedly believe it matters. I can never stress enough the importance of basing treatment on a definitive diagnosis whenever possible. While it is true small cell/low-grade alimentary LSA may be treated quite similarly to lymphoplasmacytic enteritis/IBD (with prednisolone & chlorambucil), large cell/high-grade alimentary LSA should ideally be treated with a multi-agent chemotherapy protocol (i.e. CHOP, etc.). Alternatively if your IBD patient doesn’t positively respond to initial therapies, by having a definitive diagnosis you have the ability to safely reach for another appropriate & justifiable immunomodulatory agent rather than making a best guess. Finally survival times are quite different, and in my experience, parents prefer to know this information. A well-controlled IBD cat can lead a normal & happy lifestyle, and certainly the MST for small cell LSA is better than that for large cell LSA. In my experience, when I provide parents with this information, they elect to obtain a definitive diagnosis much more often than not.

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