why bloods in lymphoma only useful for prognosis not diagnosis

[mhco]

Hi,

I have been taught that lymphoma cannot be picked up via blood tests, blood tests rather are used for prognosis, and tissue biopsy is required for diagnosis.

However why is this, as lymphoma is a proliferation of lymphocytes, shouldn't this show up as lymphocytosis in the complete blood count (if there isn't BM failure)?

So in a pt with a suitable history/examination & lymphocytosis (infx excluded) one can be pretty confident of lymphoma right?

Thanks in advance.

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[Jabbed]

I think you're confused between lymphoma and leukemia. Lymphoma will only show up on a CBC if it's in its leukemic phase, which is bad news bears for most. Additionally, the development of cytopenias also confers prognostic value (they are generally stage III/IV by that time).

If it's not in a leukemic phase, it will be missed on CBC. If the cell burden is not high enough, you won't have enough sample for flow cytometry. You also won't have any architectural histology on CBC. And finally, in general, it is best practice to biopsy malignancy at its source (lymph node).

One possible exception to the above is CLL/SLL, which is easier to think of as 'leukemia in the lymph nodes'.