Background: Leakiness of angiogenic tumor vessels results in elevated pressure in primary breast cancers and increased lymphatic flow to sentinel lymph node(s) (SLNs). We hypothesized that a similar pathophysiology in metastatic axillary SLNs would result in increased intranodal pressure (INP).
Methods: SLNs were "hot" and "blue" after intramammary injection of dilute methylene blue and filtered Tc99 sulfur colloid. Intraoperative pressure was measured in SLNs by a noncoring needle and recording device in 114 breast cancer patients. Excised axillary SLNs were examined by standard pathological techniques and metastases measured, recorded, and compared with INP measurements for SLN #1 and sometimes #2.
Results: INP in 131 SLNs with no tumor (SLN #1, n = 93; SLN #2, n = 38) was 9.1 ± 6.2 (SD; range -2, 35) mmHg and 21.4 ± 15.4 mmHg (range 0-50) in 35 tumor-containing SLNs (SLN #1, n = 29; SLN #2, n = 6) (P = 0.0066). Elevated INPs significantly correlated with SLN tumor metastasis sizes (P = 0.0038; r = 0.4904). In two patients, tumor-laden SLNs with high INP were not blue or "hot" while a blue lymphatic bypassed these nodes and was traced to the next echelon tumor-free blue and "hot" nodes with low INP.
Conclusions: Breast cancer metastasis in axillary SLNs was associated with significantly higher INP than in tumor-free lymph nodes. When "true" SLNs were replaced by tumor, and the INP levels were very high, lymph flow direction changed; lymphophilic particles (blue dye and radiocolloid) were redirected to the next echelon of nodes, where the pressures were much lower. Mechanical factors may increase the likelihood of metastasis to neighboring lymph nodes with lower INP.