THE ORDERLY PROGRESSION OF MELANOMA NODAL METASTASES

Objective The aim of this study was to determine the order of melanoma nodal metastases. Summary Background Data Most solid tumors are thoug ht to demonstrate a random nodal metastatic pattern. The incidence of skip nodal metastases precluded the use of sampling procedures of fi,s t station nodal basins to achieve adequate pathological staging. Malig nant melanoma may be different from other malignancies in that the cut aneous lymphatic flow is better defined and can be mapped accurately. The concept of an orderly progression of nodal metastases is radically different than what is thought to occur in the natural history of met astases from most other solid malignancies. Methods The investigators performed preoperative and intraoperative mapping of the cutaneous lym phatics from the primary melanoma in an attempt to identify the ''sent inel'' lymph node in the regional basin. All patients had primary mela nomas with tumor thicknesses >0.76 mm and were considered candidates f or elective lymph node dissection. The sentinel lymph node was defined as the first node in the basin from which the primary site drained. T he sentinel lymph node was harvested and submitted separately to patho logy, followed by a complete node dissection. The null hypothesis test ed was whether nodal metastases from malignant melanoma occurred in eq ual proportions among sentinel and nonsentinel nodes. Results Forty-tw o patients met the criteria of the protocol based on prognostic factor s of their primary melanoma. Thirty-four patients had histologically n egative sentinel nodes, with the rest of the nodes in the basin also b eing negative. Thus, there were no skip metastases documented. Eight p atients had positive sentinel nodes, with seven of the eight having th e sentinel node as the only site of disease, In these seven patients, the frequency of sentinel nodal metastases was 92%, whereas none of th e higher nodes had documented metastatic disease. Nodal involvement wa s compared between the sentinel and nonsentinel nodal groups, based on the binomial distribution. Under the null hypothesis of equality in d istribution of nodal metastases, the probability that all seven unpair ed observations would demonstrate that involvement of the sentinel nod e is 0.008. Conclusions The data presented demonstrate that nodal meta stases from cutaneous melanoma are not random events. The sentinel lym ph nodes in the lymphatic basins can be mapped and identified individu ally, and they have been shown to contain the first evidence of melano ma metastases. This information can be used to revolutionize melanoma care so that only those patients with evidence of nodal metastatic dis ease are subjected to the morbidity and expense of a complete node dis section. Because sentinel node histology accurately reflects the histo logy of the remainder of the lymphatic basin, information gained from the sentinel node biopsy can be used as a prognostic factor for melano ma. These findings demonstrate effective pathologic staging, no decrea se in standards of care, and a reduction of morbidity with a less aggr essive, rational surgical approach.