Expression Profiling, Protein

Expression Profiling, Protein

This grade 3 invasive carcinoma has a high mitotic rate image. Additional information is provided by the use of IHC markers to determine prognosis and guide selection of the most effective therapy.

IHC markers classify breast cancers into distinct cancer subsets that demonstrate differences in patient characteristics, prognosis, patterns of recurrence, and response to types of treatments.



  • Protein expression profiling is identification of patterns of expression that identify clinically significant subtypes of breast cancer

  • Breast cancer encompasses a group of very heterogeneous malignancies

    • Carcinomas show distinct differences in natural history, pathologic features, and biologic behavior

    • Multiple treatment options are available, including use of targeted therapies

      • Increasingly, clinical decisions on utility of treatment options and targeted therapy require assessment of underlying tumor biology

    • Need for clinically useful breast cancer classification scheme to help assess prognosis and aid treatment decisions

Breast Cancer Biology and Classification

  • Technical advances have made it possible to study underlying biology of breast cancer samples

    • Tumor tissue can be analyzed for changes at level of genome

      • DNA copy number changes; genomic gains and losses

      • Global changes in gene expression (mRNA)

      • Global changes in protein expression

  • Each of these approaches can be used to classify breast cancers into different biologic subsets

    • Biologic classification has potential to provide additional prognostic and predictive information

      • Potential aid to clinical decision making

    • Each approach has different specimen requirements

      • Some of these methodologies require fresh or snap frozen tumor samples

      • Other methodologies can be used to study formalin-fixed paraffin-embedded breast tumors


Clinically Relevant Tumor Classification

  • Classification should help distinguish different prognostic groups among patients with similar features

    • Classification should help predict response to different therapies

      • Endocrine therapies and type of endocrine therapy (e.g., tamoxifen or aromatase inhibitors)

      • Chemotherapy: Many types, doses, and combinations available

      • Biologic/targeted therapies: HER2-targeted treatment has been very successful for cancers overexpressing the protein

  • Clinically useful breast cancer classification will aid in optimal patient management

Gene Expression Profiling (GEP), mRNA

  • 4 major groups of “molecular subtypes” of cancers identified

    • 2 subgroups of ER(-) cancers

      • HER2(+) tumors with low or absent expression of ER-related genes

      • HER2(-) tumors with increased expression of basal cytokeratins

    • 2 subgroups of ER(+) cancers

      • Luminal A: High ER expression, low levels of proliferation-related gene expression

      • Luminal B: Lower levels of ER expression, high levels of proliferation-related gene expression, 1/3-1/2 overexpress HER2

  • These molecular subtypes have been confirmed as reproducible and statistically robust in independent data sets

    • Significantly correlated with prognosis, independent of traditional prognostic factors

    • Associated with different patterns of metastatic recurrence

    • May help predict likelihood of response to chemotherapy

  • Limitations of GEP

    • Clinical applicability of gene expression profiling limited

    • Requires fresh or frozen tissue

      • Only applicable for larger carcinomas for which diagnosis is known prior to surgery

      • Not suitable for small carcinomas < 1 cm

      • If tissue is harvested for this assay, reduces tumor available for histologic evaluation or other types of assays

    • Technical complexity and technical feasibility in routine practice setting

    • Reproducibility

      • Consistency of results across different laboratories or on repeat specimens has not been extensively examined

    • Cost

IHC Profiling: Single Antibodies

  • IHC evaluation of single protein markers has demonstrated clinical utility

    • ER, PR, HER2, Ki-67 (MIB-1)

    • Clinically validated as useful for risk stratification and decision for specific adjuvant therapies

      • ER and PR: Response to tamoxifen, aromatase inhibitors

      • HER2: Response to trastuzumab, lapatinib, other HER2-directed therapy

      • Ki-67: High proliferative rate may predict increased benefit from chemotherapy

  • Selected IHC antibody panels can be used to profile breast tumors

    • Able to identify breast cancer subsets with differing outcomes

    • Analytical techniques developed for GEP can be applied to IHC

  • Examination of multiple prognostic markers by IHC in well-defined cohort using unsupervised hierarchical clustering

    • Demonstrated ability to identify prognostic relevant groups of breast cancer patients

    • Determined optimal panel of IHC markers necessary to define these groups

  • Numerous investigators have attempted to “translate” gene expression data into IHC panels for clinical application in breast cancer

    • Studies suggest that application of selected antibody panels using IHC can identify breast cancer subsets with differing outcomes

      • May help predict response to specific therapies

IHC Profiling: Cytokeratin (CK) Classification

  • Breast cancers can be classified based on differential patterns of expression of cytokeratins by IHC

    • Basal subtype

      • Expression of high molecular weight “basal” cytokeratins CK5/6, CK14, CK17

      • Also frequently expresses luminal cytokeratins

    • Luminal subtype

      • Expression of low molecular weight “luminal” cytokeratins CK8, CK18

      • Usually do not express basal cytokeratins

  • Expression of basal cytokeratins in breast cancer shows a number of clinical correlations

    • Absence of ER expression

    • Aggressive clinical course with poor prognosis and increased incidence of early recurrence

      • Increased incidence of metastases to lungs and brain

    • High histological and nuclear grade with pushing borders and marked increase in proliferation

    • BRCA1-associated tumors and familial breast cancer

    • Poor responses to standard adjuvant chemotherapy

      • May be more sensitive to anthracycline-based chemotherapy compared with luminal subtype

    • Tends to occur in patients under age of 40

      • More common in premenopausal African-American and Hispanic women

IHC Profiling: Surrogates for Molecular Classification by GEP

  • Limited panel of IHC markers can identify clinically relevant groups

    • Panel includes ER, HER2, HER1 (EGFR), Ki-67, and basal cytokeratins (e.g., CK5/6)

    • Stratify breast cancer samples into subsets similar to molecular subtypes defined by expression profiling

    • Can be used as surrogate for intrinsic molecular classification of breast cancer

      • IHC surrogates for molecular subsets demonstrate similar prognostic significance compared with expression profiling

      • May be predictive for patterns of metastatic recurrence

  • Luminal A subtype

    • ER(+), HER2(-), Ki-67 low; usually PR(+)

    • Usually grade 1 or 2

    • Approximately 70% of all breast cancers

    • Metastasizes most commonly to bone; least likely subtype to metastasize to brain, liver, or lung

    • In general, shows little benefit from addition of chemotherapy to hormonal therapy

  • Luminal B subtype: HER2(-)

    • ER(+), HER2(-), Ki-67 high; may be PR(-)

    • Usually grade 2 or 3

    • Approximately 10% of all breast cancers

    • Most commonly metastasizes to bone, followed by liver and lung

    • In general, benefits from chemotherapy and hormonal therapy

  • Luminal B subtype: HER2(+)

    • ER(+), HER2(+), Ki-67 high; may be PR(-)

    • Usually grade 3

    • Approximately 10% of all breast cancers

    • Metastasizes most commonly to bone, brain, liver, and lung

    • More likely to have multicentric disease, multiple positive nodes, and higher risk of local recurrence

    • In general, benefit from chemotherapy, HER2-targeted therapy, and hormonal therapy

  • HER2 subtype

    • ER(-), HER2(+), Ki-67 high; usually PR(-)

    • Usually grade 3

    • Approximately 10% of all breast cancers

    • More likely to have multicentric disease, multiple positive nodes, and higher risk of local recurrence

    • Metastasizes most commonly to bone, brain, liver, and lung

    • In general, benefits from chemotherapy and HER2-targeted therapy but not hormonal therapy

    • Patients are younger compared to women with luminal A cancers

  • Basal subtype

    • ER(-), HER2(-), basal cytokeratin(+), EGFR(+), PR(-)

      • Identifies basal-like carcinomas defined by gene expression with 76% sensitivity, 100% specificity

      • Other IHC panels have also been used to define this group

      • Does not identify ˜ 10% that are ER positive or ˜ 10% that overexpress HER2

    • Usually poorly differentiated

    • Approximately 15% of all breast cancers

    • Less likely to have involved nodes but higher risk for local recurrence

    • Metastasizes most commonly to brain, lung, and distant nodes

    • May respond to specific types of chemotherapy

    • Patients are younger compared to women with luminal A cancers

IHC Profiling: Mammostrat® Assay

Jul 6, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Expression Profiling, Protein

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