The external axillary drainage can also be found in 20-27% of BC cases, which includes the ipsilateral internal mammary chain (17%), intramammary (3%), interpectoral (2%), and supraclavicular (2%) nodes [5].There have been accumulating knowledges that the lymphatic pathways are relatively easy to be altered after axillary lymph node (LN) dissection and/or radiation into the contralateral axilla [6, 7], paravertebral [8], or epigastric nodes [9]. Distant nonregional lymph node metastasis (DLNM) includes simultaneous and synchronous metastasis. The former indicates that metastasis existed at the initial diagnosis of breast cancer, and the latter indicates that DLNM took the form of recurrence after treatment. The two modalities are similar in proportion [10]. DLNM may be caused by the diversion and retrogradation of lymphatic drainage following the destruction of the ipsilateral lymphatic network [11-14]. Furthermore, when the original lymphatic vessels are interrupted due to surgery or radiotherapy, the lymphatic drainage may even follow collateral lymphatic channels to an alternative lymph node basin [15]. These drainage patterns could be different when compared to primary surgery and may thus result in unexpected aberrant lymphatic drainage [16]. Аberrant lymphatic spread may occasionally occur especially after occlusion of conventional pathways of lymphatic drainage following axillary dissection or irradiation [17, 18]. Lymphatic mapping seems feasible after previous BCT with axillary treatment, in spite of a relatively low identification rate [19]. Aberrant drainage patterns tend to be visualised more frequent in the group of patients after previous axillary lymph node dissection (ALND) [20].

In the clinical case presented, 6 years prior to the performance of retroperitoneal metastasis, surgical extirpation of a large supraclavicular lymph nodes with pathochistological result metastases from invasive ductal carcinoma was carried out. This surgical intervention has led to a change in lymph vessels, which we believe is the cause of para-aortic lymph node metastasis. Borst et al. reported that peritoneal and retroperitoneal metastases occurred in 0.6% of ductal carcinoma and 3.1% of lobular carcinoma cases [21]. There were 6 patients with bilateral and 4 patients with unilateral hydronephrosis. The causes of hydronephrosis were retroperitoneal metastasis in 2 cases, lymph node metastasis in 2 cases, and bladder metastasis in 6 cases. However, Guru et al. considered that the prognosis of DLNM patients is similar to that of breast cancer patients with oligometastasis [22]. Several lines of recent clinical evidence support that LN metastasis plays a significant role in systemic dissemination of cancer cells, although the effect of surgical LN dissection on survival was downplayed historically because of controversial data [23]. William Halsted proposed that breast cancer is a local disease that spreads primarily in a predictable, stepwise manner from the primary tumor to the regional lymphatics and then systemically to distant organs [24]. According to the “spectrum” theory, сancer cells develop metastatic potential as tumors grow through their clinical evolution. Accordingly, the LN involvement is of prognostic importance not only because it indicates a more malignant tumor biology, but also because persistent disease in LNs can be the source of subsequent fatal metastases [25]. For diagnosis and reporting of the tumor response, PET/CT is required, which can track in the dynamics the condition of the engaged lymph nodes (Figure 2, Figure 5). In the clinical case, we have achieved a partial healing response after 1 year of radiotherapy combined with target therapy (Figure 5) and a complete therapeutic response after 1.5 year of complex treatment (Figure 6).