Ovarian cancer remains the most lethal reproductive system cancer, with an estimated 55,000 new cases and 38,000 deaths in China in 2020 (1). According to the Chinese Cause of Death Surveillance, the crude mortality rate of ovarian cancer increased from 1.42 per 100,000 to 2.87 per 100,000 from 2006 to 2020 (2). Common symptoms in ovarian cancer patients include abdominal discomfort or distension, abdominal or pelvic pain, constipation or early satiety, weight loss, and asthenia. Inguinal lymphadenopathy is a rare initial presentation of ovarian cancer (3). Due to the usual lack of symptoms associated with early-stage disease, most cases are diagnosed only after the cancer has progressed. Epithelial ovarian cancer may metastasize intraperitoneally, lymphatically, or hematogenously (4, 5). Lymphatic dissemination from the ovary typically involves the para-aortic and pelvic areas (6), with an estimated incidence of such lesions ranging between 14% and 70% (7). Metastases to pelvic lymph nodes are less frequent than those in the para-aortic region (8–10).

The exact mechanism by which tumor cells spread to the inguinal lymph nodes remains unclear. One possibility is that tumor cells may follow the round ligament of the uterus (11) or the external iliac artery and vein. However, it has been argued that spread to the inguinal lymph nodes should only occur after the blockage of pelvic and para-aortic lymph node stations (12). Considering the peculiarity of this route of spread, the aim of this report is to describe a rare case of high-grade serous cancer of the left fallopian tube with right inguinal lymph node enlargement, with the right deep inguinal lymph nodes negative.

The patient presented with an enlarged right inguinal lymph node for at least 2 months, which was evaluated at another medical institution. She reported no other symptoms apart from occasional dull pain in the lower abdomen over the past two months. Her medical history included chronic nephritis in 2014 and the resection of a benign cervical vertebral tumor in 2021. Her family history was negative for malignancy, and she had no known occupational or environmental exposure to hormones, particularly estrogens. Clinical examination confirmed the enlarged right inguinal lymph node, which was further evaluated by abdominal ultrasound. The result revealed a heterogeneous solid mass with intrinsic vascularization, measuring 28 × 19 mm. It also showed several smaller reactive lymphadenopathies locoregionally but was otherwise normal. Laboratory analysis was normal except for an elevated CA 125 level of 46 kU/L.

A lymph node resection at the first institution revealed metastasis of high-grade serous cancer, likely from the reproductive system. A PET-CT was requested to check for other abnormalities. It confirmed a likely malignant tumor in the left adnexa, showed postoperative fluid accumulation in the right inguinal region, and revealed no other suspicious lesions or ascites. Laparoscopy showed a solid mass on the surface of the left ovary, measuring 30 × 30 × 25 mm ( Figure 1A ). The right ovary and bilateral fallopian tubes appeared normal, and no other macroscopic lesions were found in the abdominal and pelvic cavities ( Figure 1B ). There were no enlarged lymph nodes in the para-aortic or pelvic areas, and no ascites. The pathological examination revealed high-grade serous cancer in the fimbria of the left fallopian tube, which involved the left ovary, but the right deep inguinal lymph nodes were negative ( Figure 1C–H ). Germline and somatic BRCA1/2 testing showed no BRCA1 or BRCA2 mutations. The homologous recombination deficiency (HRD) status was positive, with a score of 53.44 (threshold value: 30).

According to the NCCN guidelines updated in 2024, the patient underwent six cycles of chemotherapy with Carboplatin and Taxol, administered every three weeks for the first four cycles. Bevacizumab was added to the last two cycles as her chronic nephritis was stable and her urine protein turned negative. She was subsequently placed on maintenance therapy with bevacizumab. After four cycles of chemotherapy, imaging showed no lesions. The initially elevated CA 125 level (46 kU/L) declined to 11 kU/L and remained stable.

In this report, we described a rare case of high-grade serous cancer of the left fallopian tube with right inguinal lymph node enlargement, with the right deep inguinal lymph nodes negative. Patients with ovarian cancer typically present with metastatic disease, with the most common site of metastasis being the peritoneum. Diagnosing ovarian cancer based on a metastatic inguinal lymph node is extremely rare (13). The literature reveals only a few cases where patients with ovarian carcinoma had positive inguinal lymph nodes at onset (14). Our patient initially sought medical attention for an enlarged right inguinal lymph node, and a diagnosis of high-grade serous carcinoma was made after its excision.

Metastasis to the inguinal region in ovarian cancer may occur through hematogenous spread or lymphatic spread via the round ligament (15). The lymphogenic-only spread in this case suggests a specific biological metastatic behavior. Some researchers proposed that host immune defense mechanisms may destroy the primary tumor without affecting lymphatic metastasis (16, 17), whereas others suggested that spread to the inguinal region might occur through the peritoneum after previous surgery (11), but our patient had no prior surgeries. Isolated lymph node disease in ovarian cancer appears to represent a less aggressive relapse pattern, associated with relatively mild behavior and few symptoms. According to some literature, this pattern may be related to the tumor cells’ low proliferation rate and initial lack of peritoneal spread (18). The lymph node microenvironment might keep cells dormant due to the presence of cytokines and T-cells (19). This metastatic pattern often shows higher lymphocyte infiltration, particularly of CD3 and CD8 cells, compared to extra-nodal ovarian cancer relapses. However, it does not show significant differences regarding known genomic subtypes, such as BRCA1/2 mutations or increased CCNE1 (20).

There are some limitations of the study. The current study is a single-case analysis, which restricts its broader applicability. Also, this case showed no germline or somatic BRCA1/2 mutations, and the homologous recombination deficiency (HRD) score was 53.44 (threshold value: 30). Homologous recombination deficiency may be one of the factors associated with isolated lymph node metastasis. Therefore, further research is needed to identify other genetic factors linked to this phenomenon. Specifically, the reasons for the left fallopian tube tumor presenting with right inguinal lymph node enlargement and the explanation for lymphatic drainage from the primary tumor to only the right inguinal lymph node require urgent investigation. Previous research suggests that the prognosis for this type of primary fallopian tube carcinoma (PFTC) appears to be good (14). Consequently, the patient will be followed up for a long time for clinical outcome.

The literature reports a rare case of isolated ovarian metastases to the inguinal lymph nodes, and the mechanism by which fallopian tube cancer metastasizes to the contralateral groin lymph nodes remains unclear. Homologous recombination deficiency may play an important role in this type of primary fallopian tube carcinoma (PFTC). Therefore, patients like the one in this case may benefit from PARP inhibitor (PARPi) therapy.