Lymphoma
A malignant clonal proliferation of lymphocytes that expands within lymph nodes and lymphoid tissue rather than first flooding the marrow, so it presents as painless, progressive lymphadenopathy with cytokine-driven systemic 'B symptoms', behaving very differently depending on whether the clone is Hodgkin's Reed-Sternberg cells or a non-Hodgkin subtype.
First principles
Lymphoma is a solid-tissue malignancy of the lymphoid system, which is why nodes, not the blood, are the first clue
Unlike leukaemia, the malignant clone typically arises and proliferates within a lymph node or lymphoid organ, so the earliest sign is usually a mass effect: an enlarging, typically painless lymph node. Only later, in more aggressive or advanced disease, does the marrow or peripheral blood become involved, which is why the presentation starts locally rather than with cytopenias.
Educational content pending clinical review. Not medical advice.