Seroma fluid subsequent to axillary lymph node dissection for breast cancer derives from an accumulation of afferent lymph.

Seroma is a frequent complication of breast cancer surgery, the etiology of which remains indefinite. It represents a subcutaneous accumulation of fluid frequently reported after surgical procedures such as axillary lymph node dissection. Despite previous studies have associated seroma fluid to an inflammatory exudate, the surgical removal of draining lymph nodes may indicate that seroma might not represent a mere exudate but rather an accrual of lymph drained from tributary tissues. To verify this hypothesis, seromas were collected at different intervals of time in patients operated upon for axillary lymph node removal. Fluids were analyzed in details by flow cytometry and biochemical assays for their cellular content and for their molecular features and relevant cytokine content. Lymphocytes and other peculiar blood mononuclear cells were present, while erythrocytes, platelets and granulocytes were absent or extremely rare. The protein concentration resulted lower (median 64%) than in peripheral blood. However, specific proteins related to locoregional tissues resulted highly concentrated (e.g. up to 500% for ferritin and 300% for lactate deydrogenase and exclusive presence of interleukin-6) whereas all enzymes and proteins synthesized in the liver or other organs (e.g. alkaline phosphatase, ALT, gamma GT, prealbumin, transferrin, ceruloplasmin. C3 and C4, alpha 2 macroglobulin from liver; apolipoproteins from liver and gut; amylase and lipase from pancreas) were represented in reduced concentrations, thus ruling out that seroma proteins derive directly from blood serum. As a whole, this comprehensive cytological and molecular analysis provided evidences that seroma is constituted by serum ultrafiltrated-derived extracellular fluid of regions located upstream of removed lymph nodes. This fluid is then enriched by proteins and cells collected in the drained regions. Remarkably, seroma fluids collected in the same patient at different time points (up to 50 days following surgery) displayed similar biochemical features, clearly indicating that fluid composition was not significantly affected by post-surgical locoregional flogosis. Finally, the period of seroma formation indicates that lymph accumulates in the axillary region during the interval of time needed for afferent lymphatic vessels to re-anastomose with the efferent ducts.