Palpable breast carcinomas: a hypothesis for clinically relevant lymphatic drainage in sentinel lymph node biopsy. 
Previous studies have shown that independent of tumor size, palpable breast tumors have a higher incidence of lymph node metastasis compared with nonpalpable tumors.  This study further examines this phenomenon using a large sentinel lymph node (SLN) database.  Data from a prospective, institutional review board (IRB)-approved, multi-institutional study from the University of Louisville Breast Cancer Sentinel Lymph Node Study Group was used.  From August 1997 through December 2001, 3192 patients with clinical T1 and T2 N0 breast cancer underwent SLN biopsy, most with a combined technique of radioactive colloid and blue dye, followed by level I/II axillary dissection.  Patients with palpable tumors tended to be younger (mean age 58 years) compared with nonpalpable tumors (mean age 61 years).  The incidence of positive axillary metastasis was significant between palpable and nonpalpable tumors (43% and 23%, respectively), independent of tumor size by logistic regression (p = 0.0001).  The SLN identification rate was significantly different between palpable and nonpalpable tumors (95% versus 91%, respectively; p < 0.0001).  A unifying theory to explain the phenomenon that palpable tumors, stage for stage, are associated with a higher rate of nodal metastasis is that palpable tumors are, on average, closer to the skin and the rich network of dermal lymphatics.  We believe that the dermal lymphatics of the breast represent a clinically relevant metastatic pathway to the axilla.