Her2/neu-positive disease does not increase risk of locoregional recurrence for patients treated with neoadjuvant doxorubicin-based chemotherapy, mastectomy, and radiotherapy

Hypofractionated whole breast irradiation after conservative surgery for patients aged less than 60 years: a multi-centre comparative study

Background: For decades, conventional fractionated whole breast irradiation (CF-WBI) was used after breast conserving surgery (BCS). Pivotal phase-3 trials on hypofractionated-WBI (HF-WBI) showed its non-inferiority as compared to CF-WBI. However, younger patients are often not treated with HF-WBI. The aim of this multi-centre comparative study is to confirm the safety of HF-WBI in a real-life series of younger patients.Material and methods: Between 2010 and 2016, a total of 786 patients aged less than 60 years old with early-stage breast cancer were treated with postoperative WBI after BCS in three breast cancer centres: 340 underwent HF-WBI while 446 were treated with CF-WBI. Acute toxicity was evaluated at the end of WBI. Late toxicity was evaluated at 6, 12, 24 and 36 months.Results: At univariate logistic analysis, hypofractionation showed a significant protective effect in terms of acute oedema, acute wet desquamation, chronic oedema, chronic erythema/pigmentation and breast fibrosis. At multivariate logistic analysis, hypofractionation was an independent significant factor for acute oedema, acute wet desquamation, and chronic oedema. There were not differences in tumour-related outcomes.Conclusions: HF-WBI showed significantly improved outcomes in terms of acute skin oedema, wet desquamation and chronic skin oedema. HF-WBI after BCS should be strongly encouraged to replace CF-WBI independently of age.

The prognosis comparison of different molecular subtypes of breast tumors after radiotherapy and the intrinsic reasons for their distinct radiosensitivity

Radiotherapy can increase the cell cycle arrest that promotes apoptosis, reduces the risk of tumor recurrence and has become an irreplaceable component of systematic treatment for patients with breast cancer. Substantial advances in precise radiotherapy unequivocally indicate that the benefits of radiotherapy vary depending on intrinsic subtypes of the disease; luminal A breast cancer has the highest benefit whereas human epidermal growth factor receptor 2 (HER2)-positive and triple negative breast cancer (TNBC) are affected to a lesser extent irrespective of the selection of radiotherapy strategies, such as conventional whole-breast irradiation (CWBI), accelerated partial-breast irradiation (APBI), and hypofractionated whole-breast irradiation (HWBI). The benefit disparity correlates with the differential invasiveness, malignance, and radiosensitivity of the subtypes. A combination of a number of molecular mechanisms leads to the strong radioresistant profile of HER2-positive breast cancer, and sensitization to irradiation can be induced by multiple drugs or compounds in luminal disease and TNBC. In this review, we aimed to summarize the prognostic differences between various subtypes of breast tumors after CWBI, APBI, and HWBI, the potential reasons for drug-enhanced radiosensitivity in luminal breast tumors and TNBC, and the robust radioresistance of HER2-positive cancer.

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HER2 reduces breast cancer radiosensitivity by activating focal adhesion kinase in vitro and in vivo

Growing evidence has demonstrated that human epidermal growth factor receptor 2 (HER2) is involved in the radiation response to breast cancer. However, the underlying mechanism remains elusive. Therefore, we investigated if HER2 overexpression is associated with radiosensitivity of breast cancer. We constructed breast cancer cell lines differing in HER2 expression by transducing HER2 cDNA or short hairpin RNA against HER2. We then assessed the radiosensitivity and investigated the potential mechanism by using cell proliferation assay, cell adhesion assays, anoikis assays, colony formation assays, and western blotting analyses. We found that HER2 introduction in breast cancer cell lines MCF-7 (low HER2 expression) and MDA-MB-231 (HER2 is not expressed) promoted cell proliferation and invasion and enhanced cell adhesion and resistance to anoikis. Moreover, HER2 reduced radiosensitivity in these two cells compared with the corresponding control. The opposite results were observed when HER2 was silenced in breast cancer cell lines ZR-7530 and SK-BR-3 (both cells with high expression of HER2) using HER2 shRNA. In addition, animal experiment results showed HER2 could enhance the radioresistance of xenograft tumors. Further studies showed HER2 promoted the phosphorylation of focal adhesion kinase (Fak) and thereby up-regulated the expression of proteins associated with the epithelial-to-mesenchymal transition such as Claudin-1, ZO-1, and ZEB-1. The inhibition of Fak activity using the Fak inhibitor (PF-562281) restored the radiosensitivity in HER2-overexpressing cells. In conclusion, HER2 reduces the radiosensitivity of breast cancer by activating Fak in vitro and in vivo. Fak might be a potential target for the radiosensitization of HER2-overexpressed breast cancer.

Systematic review and meta-analysis of the efficacy of breast conservation therapy followed by radiotherapy in four breast cancer subtypes

The different molecular subtypes of breast cancer are associated with distinct outcomes. We assessed the efficacy of breast conservation therapy (BCT) followed by radiotherapy for patients with different breast cancer subtypes. We searched the MEDLINE, EMBASE, and Cochrane Library databases to identify studies published prior to April 30, 2016 that assessed the efficacy of BCT followed by radiotherapy in breast cancer patients with different molecular subtypes. A meta-analysis of seven studies that included 3,798 luminal A, 770 luminal B, 344 human epidermal growth factor receptor 2 (Her-2), and 767 triple-negative breast cancer (TNBC) patients was performed. The pooled odds ratio [OR] for local relapse-free survival in luminal A compared to Her-2 patients was 0.1960 (95% confidence interval [CI]: 0.0440–0.8728, p = 0.0325) at 5 years and 0.2592 (95% CI: 0.1301–0.5167, p = 0.0001) at 10 years. The pooled OR for local-regional relapse-free survival in luminal A compared to TNBC patients was 0.1381 (95% CI: 0.0565–0.3374, p = 0.0000) at 5 years and 0.1221 (95% CI: 0.0182–0.8192, p = 0.0304) at 10 years. Thus, the rate of local-regional control is higher in luminal A patients than in Her-2 or TNBC patients.

Trastuzumab improves locoregional control in HER2-positive breast cancer patients following adjuvant radiotherapy

The benefit of adjuvant trastuzumab in disease-free and overall survival for human epidermal receptor 2-positive (HER2+) breast cancer patients is well established. However, the effect of trastuzumab on locoregional control remains unclear, particularly in patients treated with adjuvant radiotherapy (RT). In this study, we investigated the locoregional benefit of trastuzumab in patients with HER2+ breast cancer after adjuvant RT.Using a single institutional database, we identified 278 patients with stage II/III invasive HER2+ breast tumors receiving adjuvant RT between January 2008 and July 2011. We compared the locoregional outcomes of 134 patients who received trastuzumab to 144 patients without trastuzumab within the same period. Clinical and biological factors that might impact on the locoregional benefit of trastuzumab were also assessed.At the median follow-up of 45 months, trastuzumab significantly lowered the risk of locoregional recurrence (LRR) with a 3-year LRR rate of 2.4% versus 7.5% for the cohort with and without trastuzumab (P = 0.019). Trastuzumab was associated with a more significant locoregional benefit in the hormone receptor-positive (HR+)/HER2+ subgroup, with a 3-year LRR of 0% versus 6.7% in the cohort with and without trastuzumab (P = 0.027). For HR-/HER2+ breast tumor patients, the 3-year LRR rate was still lower for the cohort with trastuzumab (4.7% vs 8.6%). However, statistical significance was not found (P = 0.179). Both univariate and multivariate analyses confirmed that trastuzumab treatment was the only significant predictive factor for LRR (hazard ratio, 4.05; 95% confidence interval, 1.07-15.35; P = 0.039).Adjuvant trastuzumab in addition to RT is associated with significant reduced LRR risk in HER2+ breast cancer.

Postmastectomy radiation therapy after neoadjuvant chemotherapy: review and interpretation of available data

Postmastectomy radiotherapy (PMRT) has been shown to decrease locoregional recurrence and improve overall survival in patients with tumors greater than 5 cm or positive nodes. Because neoadjuvant chemotherapy (NAC) can cause significant downstaging, the indications for PMRT in the setting of NAC remain controversial and thus careful consideration of clinical stage at presentation, pathologic response to NAC, and other clinical characteristics, such as grade and biomarker status is required. The current review synthesizes both prospective and retrospective data to provide evidence for recommending PMRT after NAC for patients presenting with cT3-4 disease, cN2-3 disease, and residual nodal disease, as well as rationale for omitting PMRT in patients with cT1-2N0-1 disease who achieve a pathologic complete response. Other scenarios, including nodal complete response in the presence of other risk factors, are also explored. The topics of pre-NAC clinical staging and pathologic axillary nodal staging are reviewed, and radiation portal design is briefly discussed.

[Indication of radiotherapy after neoadjuvant chemotherapy in breast cancer]

Indications for adjuvant radiotherapy in breast cancer are defined from the clinical data and the pathological extent of disease in the surgical specimen. Neoadjuvant chemotherapy could modify the pathological characteristics of the tumour, inducing a pathologic complete response in 15 to 50% of cases, challenging the classical indications of adjuvant radiotherapy. The benefit of adjuvant radiotherapy after neoadjuvant chemotherapy was not prospectively evaluated. Nonetheless, from retrospective series, some recommendations with a low level of proof could be given: (i) after lumpectomy, radiotherapy of the mammary gland must be performed even in case of pathologic complete response; (ii) after mastectomy, postoperative radiotherapy is recommended in case of cT3-T4, cN1-3 (clinical or radiological) or pathologically involved nodes; (iii) irradiation of the lymph nodes areas is more questionable, but could be also proposed in case of cN1 or pN1. These recommendations are in accordance with those recently published by the National Cancer Institute and the French National Cancer Institute.

Role of postmastectomy radiation after neoadjuvant chemotherapy in stage II-III breast cancer

PURPOSE

To identify a cohort of women treated with neoadjuvant chemotherapy and mastectomy for whom postmastectomy radiation therapy (PMRT) may be omitted according to the projected risk of local-regional failure (LRF).

METHODS AND MATERIALS

Seven breast cancer physicians from the University of California cancer centers created 14 hypothetical clinical case scenarios, identified, reviewed, and abstracted the available literature (MEDLINE and Cochrane databases), and formulated evidence tables with endpoints of LRF, disease-free survival, and overall survival. Using the American College of Radiology appropriateness criteria methodology, appropriateness ratings for postmastectomy radiation were assigned for each scenario. Finally, an overall summary risk assessment table was developed.

RESULTS

Of 24 sources identified, 23 were retrospective studies from single institutions. Consensus on the appropriateness rating, defined as 80% agreement in a category, was achieved for 86% of the cases. Distinct LRF risk categories emerged. Clinical stage II (T1-2N0-1) patients, aged >40 years, estrogen receptor-positive subtype, with pathologic complete response or 0-3 positive nodes without lymphovascular invasion or extracapsular extension, were identified as having ≤ 10% risk of LRF without radiation. Limited data support stage IIIA patients with pathologic complete response as being low risk.

CONCLUSIONS

In the absence of randomized trial results, existing data can be used to guide the use of PMRT in the neoadjuvant chemotherapy setting. Using available studies to inform appropriateness ratings for clinical scenarios, we found a high concordance of treatment recommendations for PMRT and were able to identify a cohort of women with a low risk of LRF without radiation. These low-risk patients will form the basis for future planned studies within the University of California Athena Breast Health Network.

Prognostic value of breast cancer subtypes on breast cancer specific survival, distant metastases and local relapse rates in conservatively managed early stage breast cancer: a retrospective clinical study

AIM

To ascertain if breast cancer subtypes had prognostic effect on breast cancer specific survival, distant metastases and local relapse rates in women affected by early stage breast cancer.

PATIENTS AND METHODS

Data of 774 patients affected by early stage breast cancer and treated with breast-conserving therapy were reviewed. Patients were grouped, based on steroid receptor status and HER2 status as: Luminal A (ER+/PR+/HER2-), Luminal B (ER+/PR+/HER2+), Basal-like (ER-/PR-/HER2-) and HER2 (ER-/PR-/HER2+). Distribution of variables among subtypes was evaluated with Pearson's test. Survival rates were calculated with life tables; Cox regression stepwise method was used to identify predictive variables of survival.

RESULTS

Median age was 55.0 years old (range 27-80) and median follow up time of 59.0 months (range 13.6-109.7). Breast cancer specific survival and distant metastases rates were different among breast cancer subtypes (both outcomes P=0.00001) but there was no difference regarding local relapse rates (P=0.07). Axillary nodes status (P=0.00001), adjuvant therapy (P=0.03) and breast cancer subtypes (P=0.03) resulted prognostic factors of breast cancer specific survival; axillary node status (P=0.00001) and breast cancer subtypes (P=0.00001) had an impact on distant metastases. Age (P=0.003), tumor size (P=0.0001), positive or close surgical margin (P=0.00001) and tumor grade 3 (P=0.049) resulted prognostic factors of local relapse.

CONCLUSIONS

In our study, breast cancer subtype seems a prognostic factor of breast cancer specific survival and distant metastases rates, but not of local relapse rate. Patients could be submitted to conservative surgery, if feasible, but considering the differences in survivals, patients with worse prognosis should receive more aggressive adjuvant treatments.

Her-2 prognostic value in very early-stage breast cancer: a single-institution retrospective analysis

To evaluate overall survival, distant metastases-free survival and local relapse-free survival rates in a subgroup of patients affected by breast cancer expressing Her-2/neu. Data of 195 women affected by very early-stage breast cancer (pT1a-b pN0) who underwent whole breast radiotherapy after conservative surgery with or without chemotherapy and/or hormone therapy between January 2000 and December 2006 were evaluated. Chi-square test was used to compare the distribution of variables (age, tumour histology, oestrogens and progesterone receptors, tumour grading and adjuvant chemotherapy) between Her-2-positive and Her-2-negative patients. Survival rates were analysed with Kaplan-Meier curves; impact of variables on poor outcome was evaluated with Cox regression method. Median follow-up time was 63.5 months (range 13.8-113.6). Her-2/neu-positive patients (32/16.4%), compared to Her-2/neu-negative patients (163/83.6%), were younger (P = 0.0001), were affected by ductal infiltrating carcinoma (P = 0.039), had negative oestrogens receptors (P = 0.0001) and were not treated with chemotherapy (P = 0.001). Her-2-positive patients had lower overall survival (P = 0.00001) and lower distant metastases-free survival (P = 0.00001) compared to Her-2-negative patients, but no difference in local relapse-free survival was found between the two groups (P = 0.28). After multivariate analysis, Her-2-positive status was a prognostic factor for overall survival (P = 0.00001) and for distant metastases-free survival (P = 0.0001), but not for local relapse-free survival (P = 0.97). Her-2-positive patients have lower overall survival and distant metastases-free survival when compared to Her-2 negative patients but similar local relapse-free survival rates. These patients could be treated with conservative surgery, if feasible, but should receive more aggressive and tailored systemic adjuvant therapies.

Estrogen/progesterone receptor negativity and HER2 positivity predict locoregional recurrence in patients with T1a,bN0 breast cancer

PURPOSE

Data have suggested that the molecular features of breast cancer are important determinants of outcome; however, few studies have correlated these features with locoregional recurrence (LRR). In the present study, we evaluated estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) as predictors of LRR in patients with lymph node-negative disease and tumors < or = 1cm, because these patients often do not receive adjuvant chemotherapy or trastuzumab.

METHODS AND MATERIALS

The data from 911 patients with stage T1a,bN0 breast cancer who had received definitive treatment at our institution between 1997 and 2002 were retrospectively reviewed. We prospectively analyzed ER/PR/HER2 expression from the archival tissue blocks of 756 patients. These 756 patients represented the cohort for the present study.

RESULTS

With a median follow-up of 6.0 years, the 5- and 8-year Kaplan-Meier LRR rate was 1.6% and 5.9%, respectively, with no difference noted in those who underwent breast conservation therapy vs. mastectomy (p=.347). The 8-year LRR rates were greater in the patients with ER-negative (10.6% vs. 4.2%, p=.016), PR-negative (9.0% vs. 4.2%, p=.009), or HER2-positive (17.5% vs. 3.9%, p=0.009) tumors. On multivariate analysis, ER-negative and PR-negative disease (hazard ratio, 2.37; p=.046) and HER2-positive disease (hazard ratio, 3.13, p=.016) independently predicted for LRR.

CONCLUSION

Patients with ER/PR-negative or HER2-positive T1a,bN0 breast cancer had a greater risk of LRR. Therapeutic strategies, such as the use of chemotherapy and/or anti-HER2 therapies, should be considered for future clinical trials for these patients.

Breast cancer molecular subtypes in patients with locally advanced disease: impact on prognosis, patterns of recurrence, and response to therapy

Gene expression profiling has led to the discovery of 4 distinct molecular subtypes of breast cancer: luminal A, luminal B, basal like, and HER2 enriched. Investigation of these subtypes in women with breast cancer has given insight into the heterogeneous biology and outcomes in patients with locally advanced disease. These subtypes have been found to be predictors for survival, response to systemic therapy, and locoregional recurrence. This review discusses the biology of locally advanced breast cancer and the available data on how molecular subtype may provide information regarding response to treatment and prognosis of women with locally advanced breast cancer.

Does HER2 status influence locoregional failure rates in breast cancer patients treated with mastectomy for pT1-2pN0 disease?

BACKGROUND

The impact of HER2 overexpression on the locoregional control of breast cancer is controversial.

PATIENTS AND METHODS

Data on 906 women diagnosed with pT(1-2)pN(0) breast cancer from 1986 to 1992 with known HER2 status and treated with a modified radical mastectomy without adjuvant radiotherapy or adjuvant trastuzumab were analyzed with respect to local relapse-free survival (LRFS), regional relapse-free survival (RRFS) and distant relapse-free survival (DRFS). Log-rank statistics were used to compare 10-year Kaplan-Meier curves of LRFS, RRFS and DRFS in HER2+ and HER2- patients.

RESULTS

Median follow-up was 12.8 years. HER2+ patients had a worse DRFS (P = 0.028) but there was no statistically significant difference in LRFS or RRFS between HER2+ and HER2- patients (P = 0.32 and 0.24 for LRFS and RRFS, respectively). Ten-year LRFS estimates among HER2+ patients was 91.3% and 86.9% for HER2- patients. Ten-year RRFS estimates for HER2+ and HER2- patients were 88.0% and 93.0%, respectively.

CONCLUSION

HER2 overexpression was not associated with higher local or regional recurrence risk in subjects with pT(1-2)pN(0) breast cancer following mastectomy and nodal dissection after a median follow-up of >12 years.

Different criteria for HER2 positivity by IHC can be applied in post-chemotherapy specimens in determining HER2 as a prognosticator in locally advanced breast cancer

PURPOSE

We evaluated the clinical significance of HER2 in post-chemotherapy specimens after surgery in locally advanced breast cancer (LABC).

METHODS

Thirty-four patients with LABC were treated with neoadjuvant chemotherapy, surgery, adjuvant chemotherapy, and radiotherapy. The HER2 status was determined using both immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) in the paraffin-embedded surgical specimens after neoadjuvant chemotherapy.

RESULTS

The positive rate of HER2 was 41.2% and 32.4% by IHC and FISH, respectively. As the gene copy number of HER2 detected by FISH increased, the staining intensity by IHC increased with positive correlation (adjusted r (2) = 0.743; P < 0.001). According to the cutoff values of IHC score 2+ and 3+ as the positivity criteria, the concordance rates of IHC and FISH were 91.2% (31/34) and 88.2% (30/34), respectively. With the positivity criteria of IHC score > or =2+, the locoregional recurrence-free survival was better in the HER2-negative patients (P = 0.04). Trends were also found for the prolonged distant recurrence-free, disease-free, and overall survivals in the HER2-negative patients by IHC (2+). Trends for poor clinical response (P = 0.06) and more axillary nodes involvement (P = 0.08) were noted in the HER2-positive group by IHC (2+). In post-chemotherapy specimens, the positive HER2 status by IHC staining score > or = 2+ predicted higher recurrence in LABC.

CONCLUSION

This suggests that different criteria for the HER2 positivity by IHC can be applied in post-chemotherapy specimens compared with that from pre-chemotherapy biopsies.

HER-2/neu status and response to CMF: retrospective study in a series of operable breast cancer treated with primary CMF chemotherapy

PURPOSE

Primary chemotherapy brings the opportunity for an early and accurate assessment of response and offers an ideal model to search for new predictors of response. HER-2/neu is one of the most studied genes for this purpose.

PATIENTS AND METHODS

Her-2/neu was tested in a non-randomized series of 300 patients with operable breast carcinomas treated with primary CMF. Response was assessed by mammography. Disease-free survival (DFS) and overall survival (OS) were calculated after a mean follow-up of 116 months. Statistical analysis was performed to study the association between HER-2/neu status and response to CMF.

RESULTS

Overexpression/amplification was found in 23.66% cases. Univariate analysis showed that response was similar in HER-2/neu positive and negative tumors (51.38 vs. 47.36%, P = 0.6). Triple negative tumors (ER, PR and HER-2/neu negative) presented the highest response rate (64.9%). By multivariate analysis, response was significantly correlated to higher nuclear grade and negative estrogen receptor status (P = 0.02 and 0.007, respectively). Patients with HER-2/neu positive tumors presented shorter survival rates (P = 0.06). Patients with response to CMF showed a better survival over non-responders independent of Her-2/neu status. Patients with the combination of response to CMF and Her-2/neu negative tumors presented the best outcome. On the other hand, the association of no response to CMF and positive Her-2/neu score was statistically related to poor DFS and OS.

CONCLUSIONS

CMF indication is independent of Her-2/neu status.

The Impact of HER-2 Status on Local Recurrence in Women with Stage I?II Breast Cancer Treated with Breast-Conserving Therapy

This study was undertaken to determine whether overexpression of the oncogene HER-2 is associated with an increase in local recurrence in women with early stage breast cancer treated with breast-conserving therapy (BCT). A retrospective review of the medical records of all women treated with stage I-II invasive breast cancer from 1991 through 2001 was performed. Of 596 eligible patients treated in that time period, immunohistochemical testing for HER-2 expression was performed in 352 patients (59%): 266 patients (76%) were HER-2 negative and 86 patients (24%) were HER-2 positive. Median follow-up was 5.4 years. The patient characteristics for the two groups were compared for age, pathologic T and N stage, number of positive nodes, estrogen receptor (ER) and progesterone receptor (PR) status, radiation treatment, and use of hormonal therapy or chemotherapy. There were no significant differences in any of these parameters between the two groups (all p > or = 0.10). Local recurrence at 5 years was 2% in the HER-2-negative group and 0% in the HER-2-positive group (p = 0.15). There was no difference in local recurrence after BCT between HER-2-positive and negative breast cancers at 5 years. Therefore HER-2 overexpression does not appear to be a contraindication to BCT.

Radiobiology of Breast Cancer

Advances in molecular and cellular biology are transforming our understanding of breast cancer and promise the same for radiotherapy over the next few years. At the clinical level, the molecular basis of fractionation dependency and other tumour and normal tissue responses are likely to become clearer. More importantly, they will become useful in the clinic, where molecular characterisation of the patient and tumour will start to determine therapeutic options. Although many of the fundamental processes are only amenable to study in laboratory systems, the power of array-based technologies makes it possibly to address highly relevant questions in the clinic, using functional imaging and/or tissue biopsies. To help clinical oncologists exploit these opportunities in translational research, some aspects of the molecular and cellular basis of radiotherapy are described below in their relation to breast cancer.

HER2 amplification in recurrent breast cancer following breast-conserving therapy correlates with distant metastasis and poor survival

The authors analyzed the HER2 status in early-stage nonrecurrent and recurrent breast cancer groups following breast-conserving treatment. Retrospective analyses of a group of 36 invasive early breast cancer (IBC) patients who developed a local recurrence as a first event and of a random control group of 69 IBC patients were made. HER2 status was assessed by the HercepTest and fluorescence in situ hybridization. The Kaplan-Meier proportional log-rank test was used to study the impact of the biological factors on the metastasis-free interval (MFI) and the overall survival (OS). The Cox proportional hazards model, using stepwise selection was performed to identify the independent predictors of poor outcome. The median time of follow-up was 156 months (range: 22-230) for the nonrecurrent group of patients and 119 months (range: 36-228) for the recurrent group. No significant differences between either group were observed in terms of either patient or tumor characteristics, or of HER2 expression. However, a higher proportion of HER2 amplified cases were found in the recurrent group, in contrast to a higher proportion of hormonal receptor positive cases in the nonrecurrent group. After univariate and multivariate analyses, HER2 amplification was found to be an independent predictive factor for distant metastasis (HR = 10.75; p = 0.00008) and for survival (HR = 4.22; p = 0.004). In conclusion, HER2 amplification constitutes an independent poor prognostic factor for the MFI and OS in patients with recurrent breast cancer. The clinical implications are discussed.

Differential responses to doxorubicin-induced phosphorylation and activation of Akt in human breast cancer cells

INTRODUCTION

We have shown previously that overexpression of constitutively active Akt or activation of Akt caused by constitutively active Ras or human epidermal growth factor receptor-2 (HER2) confers on breast cancer cells resistance to chemotherapy or radiotherapy. As an expanded study we here report differential responses in terms of phosphorylation and activation of Akt as a result of treatment with doxorubicin in a panel of breast cancer cell lines.

METHODS

The levels of Akt phosphorylation and activity were measured by Western blot analysis with an anti-Ser473-phosphorylated Akt antibody and by in vitro Akt kinase assay using glycogen synthase kinase-3 as a substrate.

RESULTS

Within 24 hours after exposure to doxorubicin, MCF7, MDA468 and T47D cells showed a drug-dose-dependent increase in the levels of phosphorylated Akt; in contrast, SKBR3 and MDA231 cells showed a decrease in the levels of phosphorylated Akt, and minimal or no changes were detected in MDA361, MDA157 and BT474 cells. The doxorubicin-induced Akt phosphorylation was correlated with increased kinase activity and was dependent on phosphoinositide 3-kinase (PI3-K). An increased baseline level of Akt was also found in MCF7 cells treated with ionizing radiation. The cellular responses to doxorubicin-induced Akt phosphorylation were potentiated after the expression of Akt upstream activators including HER2, HER3 and focal adhesion kinase.

CONCLUSION

Taken together with our recent published results showing that constitutive Akt mediates resistance to chemotherapy or radiotherapy, our present data suggest that the doxorubicin-induced phosphorylation and activation of Akt might reflect a cellular defensive mechanism of cancer cells to overcome doxorubicin-induced cytotoxic effects, which further supports the current efforts of targeting PI3-K/Akt for enhancing the therapeutic responses of breast cancer cells to chemotherapy and radiotherapy.