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Objective To study interpectoral nodes metastasis rate in breast cancer and its clinical significance.

In a consecutive series of 73 patients undergoing a level III axillary clearance, interpectoral nodes were sought and, if palpable, excised. 18 interpectoral nodes were identified in 15 patients, 10 (14%) of whom had involved and 5 of whom had uninvolved interpectoral nodes. 7 of the 10 patients with involved interpectoral nodes also had axillary node involvement, but 3 patients had positive interpectoral nodes in the absence of involved axillary nodes. A comparison of patient and tumour characteristics in the groups of patients with and without interpectoral node involvement showed that patients who had involved interpectoral nodes were significantly younger and had significantly larger tumours. Interpectoral node involvement by breast cancer is not uncommon and these nodes can be involved in the absence of axillary nodal involvement. They should be looked for, and if identified, excised during axillary clearance.

From June to December 1990, 110 consecutive patients with breast cancer underwent a modified radical mastectomy (n=33) or quadrantectomy (n=77) combined with a complete axillary dissection and removal or interpectoral lymphatic tissue. The average number of lymph nodes removed from the axilla and interpectoral region was 22: 12.5 at Level I, 6.4 at Level II, 3.7 at Level III and 1.5 from the interpectoral tissue. In 59 110 patients fatty tissue only was found in the interpectoral region and in the remaining 51 patients, interpectoral lymph nodes were identified and these were involved in 22 patients (37.3% of total group). In 3 patients these were the only nodes involved. During axillary dissection the interpectoral space should be explored and palpable interpectoral nodes removed and submitted for histology.

Prospectively, ultrasonographic examination of the interpectoral space was performed in 185 patients with clinical and/or mammographic evidence/suspicion of breast carcinoma. Of these, 86 patients treated by modified radical mastectomy were included in the study. Interpectoral lymph node metastases were found histopathologically in 12 (14%) of patients. Ultrasonographic examination of the interpectoral space revealed enlarged Rotter's node in 4 (4.6%) of patients, and 33.3% of patients with involved interpectoral nodes. Therefore, one-third of interpectoral node involvement could be detected ultrasonographically in this group. This sonographic study represents the first report on the interpectoral region with special attention to Rotter's node.

The importance of the meticulous study by pathologists of the lymph nodes in surgical specimens is emphasized. Most pathologists identify only a small proportion of the lymph nodes in these specimens and valuable prognostic information is lost. Data illustrating the evolution in the Columbia Laboratory of surgical pathology of methods used to study surgical lymph node specimens over a 44-year period (1935--1979) are reviewed. An improved method of clearing the specimens of axillary dissections in radical mastectomy finds more lymph nodes and more metastases, and greatly shortens the time required for clearing. The importance of identifying metastases in the interpectoral nodes is emphasized. In a special study with our new clearing technique metastases were found in the interpectoral nodes in 19% of the radical mastectomy specimens. These nodes are not removed in the modified operation, which does not include resection of the pectoral muscles. The opportunity to cure a substantial proportion of patients is thus lost.