DNA copy number changes in early metastatic breast cancer lesions

A80

Axillary lymph node (LN) metastasis confers a high risk for recurrence and remains the most important predictor of prognosis in breast cancer patients. The sentinel lymph node (SLN) is the first node to harbor malignant cells in breast tumors with metastasis and currently its positivity is an indication for a complete axillary LN dissection. Because genetic alterations in the SLN lesions are likely to represent early and significant changes in the process of metastasis, characterization of such changes may aid in the discovery of new prognostic markers. In this study we investigated DNA copy number changes present in the SLN metastatic lesions and compared them to the ones present in their corresponding primary breast tumors (PBT) from the same patient. Twenty paired specimens were studied. Paraffin embedded tumor tissues were obtained from the Hospital Nossa Senhora das Gracas, Brazil, and analyzed by chromosomal comparative genomic hybridization (cCGH). We observed that there was a homogeneous distribution of the number of genomic alterations per chromosome in the PBT and in the SLN metastatic lesions (P>0.90). We also observed that the alterations observed per chromosome, as well as the number of gains and/or losses detected in the SLN lesions were significantly dependent on their incidence in the PBT (regression coefficient test; P<0.001). A non-random distribution of the number of changes was observed for all the chromosomes analyzed, both in the PBT and the SLN groups (P<0.001), respectively. The most frequent changes present in both lesions were gains of chromosomes 19, 16, 1p32~pter, 20, 17, 12q23~qter, 1q22~pter, 1q22~qter, 18p and losses of chromosomes 13q13~32, 6q13~q23, 2q22~q34. In a subset of PBT samples array-CGH (aCGH) analysis was performed and the findings were consistent with the cCGH data: alterations were detected in the genes located in the areas where gains/losses have been detected by chromosomal cCGH, including, TOP2A, AIB3, HOXB7, DLX4, HER2NEU and other genes. In conclusion, non-random chromosome alterations were observed in both lesions analyzed. The abnormalities observed in the SLN were comparable to the ones present in the corresponding PBT, indicating that those aberrations are retained during the axillary LN metastatic process. These observations suggest that the genetic alterations that control the development of axillary LN metastasis are likely to be already present in the primary tumor samples at the time of diagnosis prior to the occurrence of metastasis. Additional studies are underway in our laboratory to confirm these findings.