17q12

CD340,HER-2,HER-2/neu,HER2,MLN

Hematological malignancies

HER2 expression can be detected in blast cells from patients with hematological malignancies including acute lymphoblastic leukemia (ALL). It could be used as a potential target for the application of HER2-directed treatment strategies in ALL including vaccination approaches.

Bladder cancer

HER2 is overexpressed in 25% to 40% of several human tumors and associated with the malignancy of the disease, high mitotic index and a shorter survival time for the patient. Overexpression of ErbB-2 is also associated with transitional cell carcinoma of the bladder. HER2 overexpression occurs in muscle-invasive urothelial carcinomas of the bladder and is associated with worse survival; amplifications of erbB-2 gene are also frequently linked to alterations of the TOP2A gene in bladder cancer. Furthermore, HER2 overexpression and amplification in urothelial carcinoma of the bladder is found associated with MYC co-amplification.

Breast carcinoma

Normal tissues have a low content of HER2 membrane protein. Overexpression of HER2 is seen in 20% of breast and it confers worse biological behavior and clinical aggressiveness in breast cancer. Breast cancers can have up to 25 to 50 copies of the HER2 gene and up to a 40- to 100-fold increase in HER2 protein resulting in 2 million receptors expressed at the tumor cell surface. The differential HER2 expression between normal tissues and tumors helps to define HER2 as an ideal treatment target. Trastuzumab, the first treatment targeting HER2, is well tolerated in patients and has little toxicity because its effects are relatively specific for cancer cells overexpressing HER2. HER2 amplification is a relatively early event in human breast tumorigenesis, occurring in almost 50% of in situ carcinomas. HER2 status is maintained during progression to invasive disease and to nodal and distant metastasis. The fact that only 20% of invasive breast cancers are HER2 amplified suggests that many HER2-amplified in situ cancers never progress to the invasive stage. HER2 amplification defines a subtype of breast cancer with a unique signature of genes and this is maintained during progression. Some tumors lose HER2 expression following treatment with trastuzumab, presumably by selection of a HER2-negative clone not killed by treatment. Conversely, HER2 may become positive in some initially negative tumors over time, especially after endocrine therapy targeting ER. Indeed, estrogen receptor has been shown to downregulate HER2 and, conversely, HER2 is able to downregulate ER expression. Therefore, it is not surprising that blocking ER might upregulate HER2 and that blocking HER2 might upregulate ER. HER2-amplified breast cancers have unique biological and clinical characteristics. They have increased sensitivity to certain cytotoxic agents such as doxorubicin, relative resistance to hormonal agents, and propensity to metastasize to the brain and viscera. HER2-amplified tumors have an increased sensitivity to doxorubicin possibly due to coamplification of the topoisomerase-2 gene, which is near the HER2 locus on chromosome 17 and is the target of the drug. Half of HER2-positive breast cancers are ER positive but they generally have lower ER levels, and many have p53 alterations. These tumors have higher proliferation rates and more aneuploidy and are associated with poorer patient prognosis. The poor outcome is dramatically improved with appropriate chemotherapy combined with the HER2-targeting drug trastuzumab. Overexpression of the erbB-2 gene is associated with tumor aggressiveness, and with patient responsiveness to doxorubicin, cyclophosphamide, methotrexate, fluorouracil (CMF), and to paclitaxel, whereas tamoxifen was found to be ineffective and even detrimental in patients with HER2-positive tumors. In Pagets disease of breast, HER2 protein overexpression is caused by amplification of the erbB-2 gene. HER2 has a role in this disease of the breast, where the epidermis of the nipple is infiltrated by large neoplastic cells of glandular origin. It seems that binding of heregulin-alpha to the receptor complex on Paget cells results in chemotaxis of these breast cancer cells. The isoforms HER2p95 and HER2Δ16 are found in some breast cancers and the expression of these hyperactive forms of HER2 may contribute to the malignant progression.

Cervical cancer

HER2 may be activated in the early stage of pathogenesis of cervical carcinoma in geriatric patients and is frequently amplified in squamous cell carcinoma of the uterine cervix.

Childhood medulloblastoma

Overexpression of HER2 in medulloblastoma is associated with poor prognosis and metastasis and HER2-HER4 receptor heterodimerization is of particular biological significance in this disease.

Colorectal cancer

Overexpression of HER2 occurs in a significant number of colorectal cancers. It was significantly associated with poor survival and related to tumor progression in colorectal cancer.

Oral squamous cell carcinoma

E6/E7 proteins of HPV type 16 and HER2 cooperate to induce neoplastic transformation of primary normal oral epithelial cells. Overexpression of HER2 receptor is a frequent event in oral squamous cell carcinoma and is correlated with poor survival.

Gastric cancer

HER2 amplification/overexpression does not seem to play a role in the molecular pathogenesis of most gastrinomas. However, mild gene amplification occurs in a subset of them, and overexpression of this receptor is associated with aggressiveness of the disease. HER2 overexpression in patients with gastric cancer, and it has been solidly correlated to poor outcomes and a more aggressive disease. The overall HER2 positive rate is about 22%. HER2 overexpression rate in gastric cancer varies according to the site of the tumor. A higher overexpression rate (36%) was shown in gastroesophageal junction (GEJ) tumors in comparison to 21% in gastric tumors.

Germ-cell testicular tumor

A significant correlation was observed between HER2 overexpression and clinical outcome in germ-cell testicular tumors.

Cholangiocarcinoma

Data are still controversial about HER2 role in this carcinoma. Increased HER2 expression contributes to the development of cholangiocarcinogenesis into an advanced stage associated with tumor metastasis. In addition, overexpression of HER2 and COX-2 correlated directly with tumor differentiation. However, other studies report that HER2 expression is associated with more favorable clinical features, such as a polypoid macroscopic type and absence of other organ involvement, and has been reported that the proportion of HER2-positive cases in papillary adenocarcinoma is higher than in other histological types and is associated with an early disease stage. HER2 is preferentially expressed in well differentiated component, and it is also expressed in dedifferentiated components in progressive cases.

Lung cancer

HER2 is overexpressed in less than 20% of patients with non-small cell lung cancer (NSCLC) and studies have shown that overexpression of this receptor is correlated with a poor prognosis in both resected and advanced NSCLC. HER2 overexpression has an important function in the biology of NSCLC and may have a prognostic value for patients with metastatic NSCLC.

Higher frequency of HER2 expression has been observed in samples from patients with metastatic disease at presentation and at the time of relapse, and it correlates with worse histologic response and decreased event-free survival. HER2 could be an effective target for the immunotherapy of osteosarcoma, especially the type with high metastatic potential.

Ovarian cancer

HER2 overexpression varies from 9% to 32% of all cases of ovarian cancer and its overexpression is more frequent in advanced stage of ovarian cancer. Overexpression of HER2 in ovarian cancer cells leads to faster cell growth, higher abilities in DNA repair and colony formation. A cross-talk between HER2 and estrogen receptor (ER) was identified in ovarian cancer cells. Estrogen has been proven to induce the phosphorylation of HER2, and initiate the HER2s signaling pathway.

Pancreatic adenocarcinoma

Overexpression of HER-2 in pancreatic adenocarcinoma seems to be a result of increased transcription rather than gene amplification. The coexpression of HER2 oncogene protein, epidermal growth factor receptor, and TGF-beta1 in pancreatic ductal adenocarcinoma is related to the histopathological grades and clinical stages of tumors. The blockade of HER2 inhibits the growth of pancreatic cancer cells in vitro. HER2 overexpression was reported to accumulate in well differentiated pancreas adenocarcinomas whereas it is only infrequently found in poorly differentiated or undifferentiated tumors, in vivo and in vitro analyses have suggested that targeting HER2 might increase treatment effects of conventional chemotherapies of pancreas adenocarcinoma. However, unlike in breast cancer, the application of antibodies directed against HER2 has not yet become an established therapy for pancreas adenocarcinoma.

Prostate cancer

HER2 plays pivotal roles in prostate cancer. Studies have shown that 25% of untreated primary tumors, 59% of localized tumors after neoadjuvant hormone therapy, and 78% of metastatic tumors overexpressed HER2. Several lines of evidence have implicated HER2 as a key mediator in the recurrence of prostate cancer to a hormone-refractory, androgen-independent tumor, which is the hallmark of prostate cancer progress. The driving force for prostate cancer recurrence is the reactivation of androgen receptor (AR), which is a type of nuclear receptors, activated by steroid hormone but ablated in hormonal therapy. Phosphorylation and reactivation of AR stimulate cancer cell growth and trigger tumor progression. It has been observed that overexpression of HER2 kinase enhanced AR function and hormone-independent growth in prostate tumor cells. HER2 activated AR through the MAPK pathway. Additionally, the HER2/HER3 dimmer increases AR protein stability and promotes the binding of AR to the promoter region of its target genes, resulting in AR activation in an androgen-depleted environment.

Salivary gland tumor

Several results demonstrated significant positive staining of HER2 in the salivary tumorigenic tissue but not in the surrounding non-tumorigenic tissue, pointing to a biological role in the tumorigenic process. HER2 amplification is present predominantly in tumors with high HER2 expression and seems to be the dominant mechanism for HER2 overexpression in this tumor type.