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Department of Anatomical Pathology, PathWest, Fiona Stanley Hospital, Murdoch, WA, AustraliaDepartment of Anatomical Pathology, PathWest, QEII Medical Centre, Nedlands, WA, Australia
Hence, differentiation from primary breast cancer is important in order to individualise treatment and avoid unnecessary procedures such as radical breast surgery.
Herein, we present a rare case of endometrial stromal sarcoma (ESS) metastatic to the breast which mimicked a primary metaplastic carcinoma.
A 47-year-old woman presented with a palpable solid, irregular left breast mass. Previous medical history included a high-grade ESS with vaginal metastasis. Ultrasound showed a 24 mm solid irregular breast mass in the left breast, 9 o'clock position (Fig. 1), corresponding to a Tabar 4/5. Due to the concern for malignancy, a core biopsy was performed under ultrasound guidance.
Fig. 124 mm lesion in the left breast as seen on ultrasound.
The biopsy revealed a cellular population of plump spindled cells occurring in short fascicles, set in a mildly fibrous stroma (Fig. 2A). The cells demonstrated moderate to marked atypia in the form of enlarged, pleomorphic and hyperchromatic nuclei and easily identifiable mitoses. There was no necrosis. There was also no associated malignant epithelial/glandular component or ductal carcinoma in situ (DCIS).
Fig. 2(A) H&E stained sections of the breast biopsy with the presence of a spindle cell neoplasm. (B) Positive diffuse staining with CKAE1/3 in the breast core lesional cells. (C) H&E stained sections of the vaginal biopsy with the presence of a spindle cell neoplasm. (D) Positive diffuse staining with CKAE1/3 in vaginal biopsy lesional cells.
An extensive immunopanel was performed and showed positive staining with CKAE1/AE3 (diffuse), CKCAM 5.2 (focal) and p63 (focal) (Fig. 2B). CD10 and CyclinD1 were also added, due to the prior history of ESS, showing diffuse staining. There was no staining for ER, PR, S100, CD34, desmin and ERG. The favoured diagnosis following this immunopanel was that of a primary breast metaplastic spindle cell carcinoma, due to the extensive expression of cytokeratins.
Given the history of malignancy, the previous hysterectomy and vaginal biopsy were reviewed, confirming the prior diagnosis of ESS, metastatic to the vagina, expressing CD10 and CyclinD1 (Fig. 2C). The morphological appearances were similar to the breast tumour, prompting CKAE1/AE3 to be carried out retrospectively on the vaginal metastasis, which also showed diffuse reactivity (Fig. 2D).
Fluorescence in situ hybridisation (FISH) studies had been previously performed on the uterine tumour, revealing a disruption of BCOR at Xp11.4 with a loss of one copy of the allele in 25% of nuclei. To assist with the diagnosis of the breast lesion, FISH analysis was performed on the breast core biopsy, showing a similar signal pattern with BCOR disruption and loss of one allele in 74.5% of nuclei.
The findings overall were consistent with metastatic high-grade ESS to the breast from the uterus, associated with a BCOR gene rearrangement.
The difficulty of the pathologist in recognising metastatic lesions to the breast is often due to the lack of a prior cancer history provided by the clinician.
In our case, the valuable history of a previous metastatic ESS was communicated by the referring clinician, prompting pathological review of the histology, immunoprofile and FISH analysis of the primary uterine tumour.
The case also illustrates that diffuse cytokeratin staining in malignant spindle cell lesions of the breast should be interpreted with caution. ESS can be confused with several neoplasms due to their diverse morphological appearance and expression of a variety of immunohistochemical stains including cytokeratins.
The diffuse positive staining in our case illustrates a significant diagnostic pitfall that not all malignant breast lesions with cytokeratin positivity are primary carcinomas, with misdiagnosis likely leading to inappropriate clinical management such as wide excision/mastectomy and axillary nodal clearance.
ESS metastasising to the breast is rare. To our knowledge, there is only one other report of a breast metastasis from a low-grade ESS which occurred after a prolonged period of 17 years.
BCOR is a robust diagnostic immunohistochemical marker of genetically diverse high grade endometrial stromal sarcoma, including tumours exhibiting variant morphology.
In conclusion, we present a rare case of high-grade ESS metastatic to the breast, mimicking a primary metaplastic breast carcinoma due to extensive expression of cytokeratins. It reinforces the utility of molecular techniques and the importance of pathologists working in a multi-speciality team to guide the appropriate work-up and diagnosis of unusual and challenging cases.
Conflicts of interest and sources of funding
The authors state that there are no conflicts of interest to disclose.
References
DeLair D.F.
Corben A.D.
Catalano J.P.
et al.
Non-mammary metastases to the breast and axilla: a study of 85 cases.
BCOR is a robust diagnostic immunohistochemical marker of genetically diverse high grade endometrial stromal sarcoma, including tumours exhibiting variant morphology.
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