Primary Peritoneal High-grade Serous Carcinoma Misinterpreted as Metastatic Breast Carcinoma: A Rare Encounter in Peritoneal Fluid Cytology

Case Report

Case presentation. A 50-year-old Korean woman with a family history of breast carcinoma presented with abnormal findings in her left breast that were detected during regular screening. A subsequent biopsy led to a diagnosis of invasive ductal carcinoma of the breast. Magnetic resonance imaging (MRI) revealed an irregular spiculated mass with a diameter of 1.6 cm in the upper outer quadrant of her right breast, with adjacent probable satellite nodules. A 1.1-cm-sized non-mass enhancement was also detected in the upper outer quadrant of left breast. The patient underwent bilateral breast-conserving surgery with sentinel lymph node biopsy.

The postoperative pathological examination led to the diagnosis of multiple invasive ductal carcinomas (two right-sided; one left-sided). All lesions were defined as a modified Scarff–Bloom–Richardson grade of 2. The greatest tumor dimension was 1.5 cm. Immunohistochemistry revealed that the tumors were consistent with the luminal A subtype, as indicated by uniform estrogen receptor (ER; intensity score=3; proportion score=5; total score=8) and progesterone receptor (PR) positivity (intensity score=3; proportion score=5; total score=8) and human epidermal growth factor receptor 2 (HER2; score=0) negativity. An extensive intraductal component was present. Although lymphovascular invasion was identified, no lymph node metastasis was observed. Accordingly, the pathological stage of the breast carcinoma was pT1(3)N0. Postoperatively, the patient received chemotherapy with tamoxifen and goserelin and subsequent adjuvant radiotherapy.

Sixteen months after treatment, this patient presented at the Emergency Department with resting dyspnea. Chest computed tomography (CT) revealed right pleural thickening accompanied by a large volume of effusion in the right hemithorax, suggesting a malignancy. A cytological examination of the right-sided pleural fluid revealed numerous malignant cells, leading to a diagnosis of metastatic carcinoma. A pleural biopsy was performed via video-assisted thoracoscopic surgery (VATS), and an analysis of the specimen supported the apparent diagnosis of metastatic carcinoma. Immunostaining revealed that the pleural tumor was positive for ER but negative for PR and HER2. Accordingly, the patient underwent palliative chemotherapy with paclitaxel for pMBC.

After six cycles of palliative chemotherapy, she presented at the Emergency Department with abdominal distension. Abdominopelvic CT revealed diffuse peritoneal carcinomatosis and a large volume of ascites. The initial cytological analysis of the peritoneal fluid, as well as six subsequent analyses, yielded a diagnosis of metastatic carcinoma. At that time, polymerase chain reaction and sequencing analyses of the breast cancer 1 (BRCA1) and BRCA2 genes revealed no pathogenic mutations.

Twenty-seven months after the initial diagnosis of primary breast carcinoma, a seventh sample of peritoneal fluid was submitted for cytological examination. At that time, a gynecological pathologist examined the liquid-based cytology slides and raised a suspicion of primary peritoneal HGSC. Immunocytochemical staining to detect paired box 8 (PAX8), Wilms tumor 1 (WT1), p53, and GATA-binding protein 3 (GATA3) revealed diffuse and strongly positive staining for the former two proteins but negative staining for the latter two. These results were consistent with tubo-ovarian or peritoneal serous carcinoma. Subsequent immunostaining revealed a complete loss of p53 expression, indicative of HGSC. Finally, a diagnosis of primary peritoneal HGSC was made based on the absence of tubo-ovarian lesions on radiologic images. At that time, we repeated the BRCA mutational analysis using a multiplex ligation-dependent probe amplification method and detected a heterozygous deletion of exons 1-14 of BRCA1. Based on these results, the chemotherapy regimen was changed to paclitaxel and carboplatin for the treatment of primary peritoneal HGSC.

The patient's serum cancer antigen-125 concentration decreased rapidly following the initiation of chemotherapy (from 302.9 to 44.1 U/ml), indicating a reduced tumor burden. Two months after the change in the chemotherapy regimen, chest CT revealed no change in the extent of pleural thickening despite the disappearance of the left pleural effusion. Abdominopelvic CT revealed that although the retroperitoneal lymph node metastasis had decreased markedly in size, the mild peritoneal thickening and ascites remained unchanged. Persistent left hydronephrosis indicative of ureteral metastasis was also observed. Taken together, these findings suggested that patient had achieved a partial response.

Cytopathological findings. All liquid-based pleural and peritoneal fluid cytology specimens exhibited high cellularity. A low-power microscopic analysis revealed that the tumor cells were arranged in a predominantly papillary pattern (Figure 1A) and had formed variably sized papillary fragments and clusters with or without fibrovascular cores (Figure 1B). In some areas, individual tumor cells containing large, round-to-oval, hyperchromatic nuclei with pleomorphism and conspicuous nucleoli were admixed with mesothelial cells and inflammatory cells (Figure 1C). Mitoses were frequently observed (Figure 1D), and atypical mitotic figures were present.

The peritoneal fluid cytology specimens collected after chemotherapy contained multiple highly abnormal anaplastic nuclei that were more than five times larger than the adjacent tumor cell nuclei (Figure 1E). Most nuclei were surrounded by irregular nuclear membranes, and some displayed chromatin patterns with a smudged and degenerated appearance. Occasionally, the abnormal nuclear shape even mimicked the appearance of a multinucleated giant cell. Cells harboring these abnormal nuclei also possessed intracytoplasmic microvacuoles (Figure 1F), the aggregates of which resulted in a foamy appearance. Some tumor cells also contained large intracytoplasmic vacuoles that resembled perinuclear halos. Cyst-like spaces were observed between the individual tumor cells (Figure 1G).

Immunostaining of cell blocks and liquid-based preparation slides was performed as previously described (4-15). Immunocytochemically, the tumor cells exhibited diffuse and strong nuclear immunoreactivity for PAX8 (Figure 1H) and WT1 (Figure 1I), indicating a Müllerian origin and serous type, respectively. However, malignant cell nuclei completely lacked p53 expression (Figure 1J), indicating a truncating TP53 mutation. The lack of immunoreactivity for GATA3 (Figure 1K) excluded the possibility of a metastasis originating from the breast carcinoma.

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Figure 1.

Cytopathological observations of liquid-based preparations of pleural and peritoneal fluid specimens. A: High cellularity with papillary architecture. B: Variably sized papillary fragments and clusters, with or without fibrovascular cores. C: Large, round-to-oval hyperchromatic nuclei with pleomorphism and conspicuous nucleoli. D: Frequent mitoses. E: Chemotherapy-induced atypia, including highly abnormal anaplastic nuclei more than 5 times larger than the adjacent tumor cell nuclei. Chemotherapy-induced atypia included intracytoplasmic microvacuoles (F) and large intracytoplasmic vacuoles (G) that formed perinuclear haloes and cyst-like spaces. Strong, uniform nuclear paired box 8 (H) and Wilms tumor 1 (I) expression was apparent. J: There was complete absence of p53 expression, indicating TP53 mutation. K: Lack of nuclear GATA-binding protein 3 expression was noted. Liquid-based preparation. A to G, Papanicolaou staining; H to K, polymer method. Original magnification, A, ×40; B, ×100; C, ×200; D, ×400; E to G, ×600; H to K, ×400.

Histopathological findings. The VATS pleural biopsy specimen revealed diffusely growing tumor cells and a lack of papillary architecture. Irregularly shaped and sized clusters of tumor cells were delineated by infiltrating borders containing obviously desmoplastic stroma (Figure 2A). The individual tumor cells exhibited both cytoplasmic and nuclear alterations and possessed relatively distinct borders with abundant eosinophilic cytoplasm. In several foci, the cytoplasm was either intensely eosinophilic or clear, with variably-sized vacuoles. The tumor cell nuclei displayed marked pleomorphism and membrane irregularity. Consistent with the cytopathological features, some tumor cell nuclei were more than 5-fold larger than those in the adjacent tumor cells, and cells harboring the former nuclei thus resembled multinucleated giant cells (Figure 2B). These cells also had a degenerated appearance, with apparent chromatin clumping or smudging. Frequent mitotic figures and a few atypical mitoses were observed. Consistent with the cytology specimens, occasional intracytoplasmic vacuoles were detected. Coagulative tumor cell necrosis was evident in some areas of the biopsied specimen, and scattered nests or clusters of surviving tumor cells were observed adjacent to the necrotic areas (Figure 2C). Lymphatic tumor emboli were also identified. The stroma was densely fibrotic in some areas and contained inflammatory cells and fibrinous debris. Immunostaining of the pleural tumor yielded results consistent with the immunocytochemical findings. Specifically, the tumor cells were uniformly positive for PAX8 (Figure 2E) and WT1 (Figure 2F), and exhibited a complete lack of p53 expression (Figure 2G). The surrounding inflammatory cells and reactive mesothelial cells exhibited patchy p53 expression with a variable level of staining intensity (i.e. wild-type p53 expression pattern). Again, the tumor cells were negative for GATA3 (Figure 2H), as well as cytokeratin 5/6 and D2-40, which excluded the possibility of MBC and malignant mesothelioma.

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Figure 2.

Histopathological findings of a pleural biopsy obtained via video-assisted thoracoscopic surgery. A: Diffusely growing tumor cells were found, devoid of papillary architecture. They were variably sized, irregularly shaped clusters of tumor cells with infiltrating borders and obvious desmoplastic stroma. B: Intensely eosinophilic or clear cytoplasm with variably sized vacuoles, markedly pleomorphic nuclei with irregular membranes was noted, and with frequent mitotic figures and a few atypical figures. C: Coagulative tumor cell necrosis and nests or clusters of surviving tumor cells were apparent. Cells showed strong, uniform nuclear paired box 8 (D) and Wilms tumor 1 (E) expression. F: p53 Expression was completely absent, indicating TP53 mutation. G: Lack of nuclear GATA-binding protein 3 expression was noted. A to C, hematoxylin and eosin staining; D to G, polymer method. Original magnification, A, ×100; B, ×400; C, ×100; D to G, ×200.