Expression of LRP and MDR1 in locally advanced breast cancer predicts axillary node invasion at the time of rescue mastectomy after induction chemotherapy

Background: Axillary node status after induction chemotherapy for locally a dvanced breast cancer has been shown on multivariate analysis to be an inde pendent predictor of relapse. However, it has been postulated that responde rs to induction chemotherapy with a clinically negative axilla could be spa red the burden of lymphadenectomy, because most of them will not show histo logical nodal invasion. P-glycoprotein expression in the rescue mastectomy specimen has finally been identified as a significant predictor of patient survival. Materials and methods: We studied the expression of the genes encoding mult idrug resistance associated protein (MDR1) and lung cancer associated resis tance protein (LRP) in formalin-fixed, paraffin-embedded tumor samples from 52 patients treated for locally advanced breast cancer by means of inducti on chemotherapy followed by rescue mastectomy. P-glycoprotein expression wa s assessed by means of immunohistochemistry before treatment in 23 cases, a nd by means of reverse-transcriptase-mediated polymerase chain reaction (RT -PCR) after treatment in 46 (6 failed). LRP expression was detected by mean s of immunohistochemistry, with the LRP-56 monoclonal antibody, in 31 cases before treatment. Immunohistochemistry for detecting the expression of c-e rb-B2, p53, Ki67, estrogen receptor and progesterone receptor are routinely performed in our laboratory in every case, and the results obtained were i ncluded in the study. All patients had received between two and six cycles of standard 5-fluorouracil, doxorubicin and cyclophosphamide (FAC) chemothe rapy, with two exceptions [one patient received four cycles of a docetaxel- adriamycin combination, and the other four cycles of standard cyclophospham ide-methotrexate-5-fluorouracil (CMF) polychemotherapy]. Response was asses sed in accordance with the Response Evaluation Criteria In Solid Tumors (RE CIST), By these, 2 patients achieved a complete clinical response, 37 a par tial response, and the remaining 13 showed stable disease. This makes a tot al clinical response rate of 75.0%. None achieved a complete pathological r esponse. Results: MDR1 mRNA expression detected by RT-PCR was associated with the pr esence of invaded axillary nodes at surgery in 18/22 cases (81.8%), compare d with 13/24 (54.2%) in the group with undetectable MDR1 expression. This d ifference was statistically significant (P < 0.05). LRP expression in more than 20% of tumor cells before any treatment was associated with axillary n odal metastasis after chemotherapy and rescue mastectomy in 17/23 cases, co mpared with 3/8 in nonexpressors. Again, this difference was highly signifi cant (P< 0.01). LRP expression before treatment and MDR1 mRNA expression af ter treatment were significantly interrelated (P< 0.001), which might refle ct the presence of chemoresistant clones liable to metastasize to the regio nal nodes. Persistence of previously detected MDR1-positivity after treatme nt (7/9 compared with 0/2 cases) was significantly associated with axillary node metastasis (P< 0.05). Finally, in a logistic regression multivariate model, histology other than ductal, a Ki67 labeling index of at least 20% a nd the combination of LRP and MDR1 positivity emerged as independent predic tors of axillary node invasion at the time of rescue mastectomy. Conclusion: The expression of different genes involved in resistance to che motherapy, both before and after treatment with neoadjuvant, is associated with the presence of axillary node invasion at rescue surgery in locally ad vanced breast cancer. This might reflect the presence of intrinsically resi stant clones before any form of therapy, which persist after it, and could be helpful both for prognosis and for the choice of individual treatment.