Cytopathology in Focus: Use of cytologic samples to assess predictive biomarkers in metastatic breast cancer

Shahla Masood, MD
Anwer Siddiqi, MD, MS

May 2024—Breast cancer continues to remain a major global health issue and one of the main leading causes of cancer mortality among women worldwide. The majority of breast cancer mortality is attributed to its ability to metastasize. Bone, lung, liver, pleura, and brain are the most common sites of metastatic lesions, often spreading from invasive breast carcinoma of no special type. On the other hand, invasive lobular carcinoma most commonly metastasizes to gastrointestinal and gynecologic organs, peritoneum, leptomeninges, bone marrow, thyroid, and adrenal glands. Aside from a clinical history of primary breast cancer, morphologic features and the pattern of immunostaining for TRPS1, GATA-3, and mammaglobin can support a diagnosis of metastatic breast cancer. In addition to the need for an accurate morphologic diagnosis of a metastatic breast carcinoma, there is also a need to assess the pattern of expression of predictive biomarkers in metastatic lesions of breast for further choice of therapeutic options.

Currently, any superficial and most deep-seated metastatic lesions can be sampled easily by fine-needle aspiration biopsy (FNAB) or core needle biopsy (CNB). Cellular material and tumor tissue obtained via nonsurgical sampling of metastatic lesions frequently provide adequate samples for determining the status of estrogen receptor, progesterone receptor, and HER2/neu. FNAB is a well-established procedure that is often used to determine the status of regional lymph node metastasis with or without image guidance. The information obtained from this technique is used to assess the decision of performing sentinel lymph node biopsy versus axillary node dissection, as well as to make a therapeutic decision for presurgical neoadjuvant chemotherapy. This sampling procedure is also effectively used for the diagnosis and assessment of the pattern of expression of biomarkers in distant metastasis of breast carcinoma. In deep-seated lesions such as breast metastasis to the bones, FNAB is most effective as it bypasses the decalcification step used in CNB. Decalcification of breast tumor samples may result in decreased expression of biomarkers.

Metastatic tumor cells can be seen in cerebrospinal fluid cytology; in pleural, peritoneal, and pelvic cavity; in bronchoalveolar lavage; and rarely in urine cytology. We previously reported our experience in FNAB, core imprint, cytospin preparations, and body fluid cell block preparations and confirmed that these samples can be used effectively for biomarker studies. The results of these studies have often correlated positively with the results of biomarker status of primary tumor sites.

Biomarker analysis in cytology samples. Estrogen receptor, progesterone receptor, and HER2/neu, collectively referred to as the breast cancer biomarkers, are the cornerstone of the information reported by the pathologists/cytopathologists for patients with breast cancer and are the basis for oncologists to offer individualized therapeutic options for patients with metastatic breast cancer. Currently, biomarker testing is recommended for every metastatic breast cancer site.

Reports in the literature have shown a difference of expression for estrogen receptor and HER2/neu in up to 16 percent and 10 percent between primary and metastatic breast cancer, respectively. Aside from the existing heterogeneity of expression of these biomarkers, the actual differences in the test results require the revision of therapeutic intervention in patients with metastatic breast cancer. The samples obtained by minimally invasive procedures and exfoliative cytology provide sufficient material for diagnosis and evaluation of biomarkers in metastatic breast cancer.

The challenge of analysis of cytologic preparation for assessment of predictive biomarkers is the lack of validation of processing and interpretation of these test results. However, there is evidence suggesting strong correlation of test results between histology specimen versus cytologic preparation. Other challenges include the effect of different fixatives used in liquid-based collection systems and different cell block preparations. However, several studies have shown promising results in the use of cytologic preparations for predictive biomarker testing. Based on ASCO/CAP guidelines, for assessment of breast biomarkers, ischemic time (between the removal of the sample from the patient and placing it in 10 percent formalin fixation) should be less than one hour. In addition, the specimen should be fixed in formalin for at least six hours, and no greater than 48 hours for HER2/neu testing and no greater than 72 hours for estrogen and progesterone receptors.

It is also critically important that every department follow its established procedures with sufficient quality control measures to make sure that the results of breast cancer biomarkers reflect the actual status of expression or gene amplification of these entities for every given patient. In addition, as more predictive biomarkers will be identified and more targeted therapies become available, the role of cytopathology in providing accurate test results for all patients with breast cancer will become necessary.

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Dr. Masood is professor and chair of the Department of Pathology and Laboratory Medicine, University of Florida College of Medicine, Jacksonville, and a member of the CAP Cytopathology Committee. Dr. Siddiqi is associate professor at the University of Florida College of Medicine.