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In this issue of the journal, van Deurzen et al report on the occurrence of in transit (interval or intercalated) lymph node metastasis in breast cancer (see page 1314).1 The phenomenon they describe relates to small lymph nodes which were recognised as lymph nodes only during step sectioning of the afferent lymphatic vessels that had also been removed during sentinel lymph node (SLN) biopsy. Of 17 patients investigated, three demonstrated such in transit nodes, connected to the afferent lymphatic of the SLN, and one of these nodes contained a small metastasis measuring 3.4 mm. Although the specific patient also had metastasis in the SLN, and her therapy was not influenced by the finding, the authors propose that such nodal deposits might be the sources of locoregional recurrence.
The term in transit metastasis comes from the melanoma practice, and the authors also refer to the similarity of the reported phenomenon with the in transit metastasis of melanoma. However, in transit metastases of melanoma are defined as recurrences/metastases developing between the site of the primary tumour (at least 2 cm away from it to arbitrarily distinguish them from satellite lesions, which have the same prognostic impact than in transit lesions) and the regional lymph nodes. They are generally not associated with lymph nodal structures, despite the fact that they are listed among the pN categories of the TNM classification.2 3 They are intralymphatic at the beginning and develop from lymphatic emboli. Such lymphatic emboli are the sine qua non of lymphogenic metastases in all organs, and lymphangiogenesis may contribute to their increased frequency in melanoma.4 Although lymphangiogenesis could not be documented in primary breast carcinomas,5 6 it may still play some role in it,7 and the presence of lymphatic invasion in breast cancer is associated …