Inguinal lymph node metastasis from breast cancer is extremely rare [10,11,12,13]. Immunohistochemistry demonstrated the positive expression of CK7 and ER, and the absence of CK20 in our case. These expressions indicate the possibilities of gastrointestinal and urinary origins to be substantially excluded from the inguinal metastases. On the contrary, most of the breast cancers show these expression patterns [7, 8]. Additionally, mammaglobin was also positive in this case of inguinal metastases. Mammaglobin is reported to be the most reliable mammary-specific markers of which sensitivity and specificity are 84.3% and 85.0%, respectively . Intriguingly, the series of CTs retrospectively reviewed showed the correlation of the growing patterns between the breast tumor and the inguinal lymph nodes (Fig. 2a, b). The dormancy of the swelling after the breast operation could be caused by the effect of the subsequent hormone therapy (Fig. 2c). Taking these immunohistochemical results as well as the course of progressing pattern of inguinal nodes into consideration, we diagnosed the present case as breast cancer origin. In our knowledge, this is the sixth reported case in English literature.
The first such report by Baba et al.  described a patient with inguinal node swelling preceding the ipsilateral breast lump by a year. She received intensive treatments including curative operations, chemotherapy, and radiation to the inguinal region. However, 32 months after the breast surgery, marked lymph node metastases recurred in the pelvis. She succumbed due to the entire organ metastases thereafter. The authors proposed two probable pathways to the inguinal lymph node metastasis: a direct pathway through skin or subcutaneous lymphatic vessels, or a retrograde pathway through submuscular fascia when axillary lymph nodes were blocked. Goyal et al.  also presented a case of right inguinal lymph node metastasis, 3 years after bilateral triple negative breast cancers. Local irradiation and taxane-based systemic chemotherapy were applied. Two years later, the developing extensive retroperitoneal and pelvic nodal metastases induced the patient to expire. The authors also speculated altered lymphatic pathways could have been responsible for the inguinal involvement.
There have been accumulating knowledges that the lymphatic pathways are relatively easy to be altered after axillary lymph node dissection and/or radiation [1,2,3,4,5]. Surprisingly, alteration of lymphatic pathways into the contralateral axilla [1, 2, 4, 5], paravertebral , or epigastric nodes  have been reported. Sato et al.  elucidated that either axillary dissection or radiation increased the rate of aberrant lymphatic drainage by examining the re-sentinel lymphoscintigraphy for the patients with ipsilateral breast cancer recurrences. Nine out of 17 patients (64.3%) receiving both axillary dissection and radiation showed the lymphatic drainage pattern into the contralateral axilla. Kaur et al.  examined 45 patients previously undergone breast-conserving surgery and complete ALND, who subsequently had reoperation for ipsilateral breast recurrence. Thirteen (29%) cases had a successful SLN biopsy, among which 5 cases were identified as showing non-axillary drainages: 3 in internal mammary and 2 in contralateral axillary nodes. Indeed, two out of 5 patients ended up being metastatic.
In the present case, however, the inguinal node metastases preceded the breast surgery. It is presumable that stagnated and elusive axillary lymphatics had already been existing preoperatively. The postoperative intractable lymphatic discharge shown in this case could be due to preexisting the stagnation of centrally heading lymphatic pathways. Additionally, the previously performed meticulous abdominal operations, her history of congenital hip location and extraordinary obesity could influence the changing lymphatic pathways. As there was no retroperitoneal or internal iliac lymph node metastasis, we speculate an alternate pathway through the body surface could be plausible. It probably passed from the subcutaneous or submuscular fascia to the contralateral epigastric lymphatics through the developed lymphatic networks by the previous five times’ abdominal operations and reached the superficial inguinal lymph nodes.
We acknowledge this is the first case of contralateral inguinal metastases from breast cancer reported in English literature. We need to mention that not only breast operation or radiation therapy, but abdominal surgery could cause alteration of the lymphatic flows of breast cancer. As shown in the previous cases, the prognoses of these patients were poor. Our patient has now been treated only by anti-estrogen therapy for adjuvant remedy due to her poor ADL and progressing dementia. Further continuous prudent follow-ups should be mandatory in the future.