# Isolated low-grade serous carcinoma arising in inguinal lymph nodes in the setting of endosalpingiosis: A case report

## TL;DR

A rare case of low-grade serous carcinoma in the inguinal lymph node, arising from endosalpingiosis, highlights the importance of accurate diagnosis to avoid mismanagement.

## Contribution

Reports a rare case of primary inguinal node LGSC arising from endosalpingiosis, emphasizing diagnostic challenges and treatment implications.

## Key findings

- LGSC can present in isolated extra-ovarian sites like inguinal lymph nodes.
- Initial misdiagnosis as HGSC can lead to ineffective treatment.
- Accurate histopathology and molecular profiling are essential for correct classification.

## Abstract

•Low-grade serous carcinoma (LGSC) can arise in isolated extra-ovarian locations, including inguinal lymph nodes.•Accurate histopathologic diagnosis, including IHC and molecular profiling, is critical in distinguishing LGSC from HGSC.•Misclassification of serous carcinomas can lead to inappropriate treatment strategies and delayed definitive management.•Recognition of endosalpingiosis and its potential malignant transformation is important in evaluating gynecologic lesions.•Treatment of isolated extra-pelvic LGSC lesions should mirror that of more common adnexal disease.

Low-grade serous carcinoma (LGSC) can arise in isolated extra-ovarian locations, including inguinal lymph nodes.

Accurate histopathologic diagnosis, including IHC and molecular profiling, is critical in distinguishing LGSC from HGSC.

Misclassification of serous carcinomas can lead to inappropriate treatment strategies and delayed definitive management.

Recognition of endosalpingiosis and its potential malignant transformation is important in evaluating gynecologic lesions.

Treatment of isolated extra-pelvic LGSC lesions should mirror that of more common adnexal disease.

Low-grade serous carcinoma (LGSC) is a rare, indolent subtype of epithelial ovarian cancer that often arises from precursor lesions in the ovary or peritoneum and is associated with MAPK pathway mutations. Unlike high-grade serous carcinoma (HGSC), which typically originates from cells in the fallopian tube, LGSC shows limited response to chemotherapy. An isolated presentation in an extraperitoneal site, such as an inguinal lymph node, is exceedingly rare. We present a case of primary nodal LGSC arising in the setting of endosalpingiosis.

An 80-year-old woman presented with a two-year history of left lower quadrant pain and a newly enlarging left groin mass. Imaging identified a vascular left inguinal mass, and initial biopsy favored HGSC. Staging procedures including hysteroscopy, dilation and curettage, and diagnostic laparoscopy with bilateral salpingo-oophorectomy showed normal pelvic organs with no evidence of malignancy. Chemotherapy was initiated but resulted in only a modest response. Surgical resection of the mass itself revealed LGSC with adjacent endosalpingiosis. With no evidence of primary disease elsewhere, a diagnosis of primary inguinal node LGSC arising from endosalpingiosis was made.

This case highlights the diagnostic challenges of isolated LGSC without a detectable primary site. Initial misclassification can lead to suboptimal management. Accurate diagnosis requires thorough surgical and pathological evaluation to ensure appropriate treatment in these rare and atypical presentations.