RT-PCR for Mammaglobin Genes, MGB1 and MGB2, Identifies Breast
RT-PCR for Mammaglobin Genes, MGB1 and MGB2, Identifies Breast
In the present study, we examined the expression of the mammaglobin genes, MGB1 and MGB2, in the sentinel lymph nodes (SLNs) of patients with breast cancer and compared our results with the histologic status of the same SLNs. Compared with immunohistochemical staining for cytokeratin 8, which detected metastases in 17 of 42 patients, reverse transcription-polymerase chain reaction (RT-PCR) for MGB1 or MGB2 genes was positive in 22 patients. The concordance between the expression of any mammaglobin and histologic status was 79% (33/42), with a sensitivity of 88% and specificity of 72%. The detection of patients with metastases was more sensitive when testing for both MGB1 and MGB2 (P < .0001) rather than MGB2 (P < .0005) or MGB1 (P < .05) alone. The increased detection rate relative to histologic examination suggests that using RT-PCR for the mammaglobin genes might identify patients at higher risk compared with patients with negative RT-PCR results.
The sentinel lymph node (SLN) biopsy is becoming an alternative to complete axillary lymph node (ALN) dissection in the staging of breast cancer. Initially applied to patients with melanoma and, subsequently, to patients with breast cancer, the SLN concept is based on the rationale that SLNs should be the first nodes to receive primary lymphatic flow from the tumor and, therefore, should be more likely to contain disseminated tumor cells than would non-SLNs. Intraoperative identification of SLNs is achieved by the injection of vital dyes, radiolabeled colloids, or both in the peritumoral area before lymph node dissection. One important advantage of the SLN biopsy is that it spares patients without metastasis from complete ALN dissection and its associated morbidity.
Consistent with the hypothesis that SLNs should not harbor metastases when the remaining nodes are free of metastases, previous studies have demonstrated that the histologic status of SLNs using routine histologic examination reflects that of ALNs with 96% to 100% accuracy. Other studies involving more extensive and focused pathologic analysis of SLNs have revealed that the diagnostic accuracy was improved significantly. Indeed, serial sectioning, immunohistochemical analysis, and a combination of both have been found to increase the detection rate of SLN micrometastases that had been missed by using standard H&E staining. However, the number of patients with positive nodes with tumors up-staged by the combination of serial sectioning and immunohistochemical analysis does not account for all patients with negative nodes who experience relapse and eventually die of the disease. Even if all metastatic SLNs could be identified, application of these techniques to all SLNs is too labor-intensive and costly to be used for routine examination. Clearly, a technique that is at once more sensitive and simple is needed for accurate staging of breast cancer.
The reverse transcription-polymerase chain reaction (RT-PCR) has proven to be a highly sensitive diagnostic tool in the detection of lymph node metastases in patients with breast cancer. Genetic markers such as MUC1, CK19, and CEA (carcinoembryonic antigen) have been shown to increase the number of positive lymph nodes compared with immunohistochemical staining. The specificity and diagnostic value of these markers, however, remain controversial because they have been reported to be present and absent in lymph nodes from patients without cancer.
Mammaglobin (MGB1) and mammaglobin B (MGB2) are 2 related genes of the uteroglobin gene family that are overexpressed in breast tissue and metastatic lymph nodes from patients with breast cancer. While MGB1 is expressed specifically in breast tissue, MGB2 expression also is found in the uterus and salivary gland. Recent studies using RT-PCR assays have revealed high levels of expression of MGB1, MGB2, or both in human breast cancer cell lines and metastatic lymph nodes, with an absence in noncancerous tissues. Compared with histologic results, markers for MGB1, MGB2, or both increase the number of positive lymph nodes detected. Because of their high specificity and sensitivity, MGB1 and MGB2 markers might be ideal candidates for screening patients with breast cancer. To our knowledge, no single study has studied the dual use of MGB1 and MGB2 markers in SLNs. In the present study, patients with breast cancer underwent surgical removal of SLNs, and the expression of MGB1 and MGB2 was examined using RT-PCR. The RT-PCR results were compared with those obtained by immunohistochemical analysis and serial sectioning of the same SLNs.
In the present study, we examined the expression of the mammaglobin genes, MGB1 and MGB2, in the sentinel lymph nodes (SLNs) of patients with breast cancer and compared our results with the histologic status of the same SLNs. Compared with immunohistochemical staining for cytokeratin 8, which detected metastases in 17 of 42 patients, reverse transcription-polymerase chain reaction (RT-PCR) for MGB1 or MGB2 genes was positive in 22 patients. The concordance between the expression of any mammaglobin and histologic status was 79% (33/42), with a sensitivity of 88% and specificity of 72%. The detection of patients with metastases was more sensitive when testing for both MGB1 and MGB2 (P < .0001) rather than MGB2 (P < .0005) or MGB1 (P < .05) alone. The increased detection rate relative to histologic examination suggests that using RT-PCR for the mammaglobin genes might identify patients at higher risk compared with patients with negative RT-PCR results.
The sentinel lymph node (SLN) biopsy is becoming an alternative to complete axillary lymph node (ALN) dissection in the staging of breast cancer. Initially applied to patients with melanoma and, subsequently, to patients with breast cancer, the SLN concept is based on the rationale that SLNs should be the first nodes to receive primary lymphatic flow from the tumor and, therefore, should be more likely to contain disseminated tumor cells than would non-SLNs. Intraoperative identification of SLNs is achieved by the injection of vital dyes, radiolabeled colloids, or both in the peritumoral area before lymph node dissection. One important advantage of the SLN biopsy is that it spares patients without metastasis from complete ALN dissection and its associated morbidity.
Consistent with the hypothesis that SLNs should not harbor metastases when the remaining nodes are free of metastases, previous studies have demonstrated that the histologic status of SLNs using routine histologic examination reflects that of ALNs with 96% to 100% accuracy. Other studies involving more extensive and focused pathologic analysis of SLNs have revealed that the diagnostic accuracy was improved significantly. Indeed, serial sectioning, immunohistochemical analysis, and a combination of both have been found to increase the detection rate of SLN micrometastases that had been missed by using standard H&E staining. However, the number of patients with positive nodes with tumors up-staged by the combination of serial sectioning and immunohistochemical analysis does not account for all patients with negative nodes who experience relapse and eventually die of the disease. Even if all metastatic SLNs could be identified, application of these techniques to all SLNs is too labor-intensive and costly to be used for routine examination. Clearly, a technique that is at once more sensitive and simple is needed for accurate staging of breast cancer.
The reverse transcription-polymerase chain reaction (RT-PCR) has proven to be a highly sensitive diagnostic tool in the detection of lymph node metastases in patients with breast cancer. Genetic markers such as MUC1, CK19, and CEA (carcinoembryonic antigen) have been shown to increase the number of positive lymph nodes compared with immunohistochemical staining. The specificity and diagnostic value of these markers, however, remain controversial because they have been reported to be present and absent in lymph nodes from patients without cancer.
Mammaglobin (MGB1) and mammaglobin B (MGB2) are 2 related genes of the uteroglobin gene family that are overexpressed in breast tissue and metastatic lymph nodes from patients with breast cancer. While MGB1 is expressed specifically in breast tissue, MGB2 expression also is found in the uterus and salivary gland. Recent studies using RT-PCR assays have revealed high levels of expression of MGB1, MGB2, or both in human breast cancer cell lines and metastatic lymph nodes, with an absence in noncancerous tissues. Compared with histologic results, markers for MGB1, MGB2, or both increase the number of positive lymph nodes detected. Because of their high specificity and sensitivity, MGB1 and MGB2 markers might be ideal candidates for screening patients with breast cancer. To our knowledge, no single study has studied the dual use of MGB1 and MGB2 markers in SLNs. In the present study, patients with breast cancer underwent surgical removal of SLNs, and the expression of MGB1 and MGB2 was examined using RT-PCR. The RT-PCR results were compared with those obtained by immunohistochemical analysis and serial sectioning of the same SLNs.
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