Gene expression profiling and expanded immunohistochemistry tests for guiding adjuvant chemotherapy decisions in early breast cancer management: MammaPrint, Oncotype DX, IHC4 and Mammostrat

The individual tests: MammaPrint, Oncotype DX, IHC4, Mammostrat

4.1 Gene expression profiling and immunohistochemistry tests typically report 1 or 2 types of information – breast cancer subtype and risk of recurrence. Tests developed to provide information on subtypes can be used either before surgery to inform decisions on neoadjuvant therapy or after primary surgery (for removal of the tumour, which may also be used for further assessment of the tumour characteristics) to inform decisions on adjuvant chemotherapy (see figure 1). Tests predicting the risk of recurrence in a specific population are typically used after surgery, in conjunction with other information such as tumour size and grade, to guide the use of adjuvant chemotherapy. Such tests are typically indicated for women with oestrogen receptor positive (ER+) and lymph node negative (LN−) (and sometimes LN+ if the number of nodes is small) breast cancer in whom there is significant uncertainty about the value of chemotherapy. The current evaluation addresses the use of MammaPrint, Oncotype DX, IHC4 and Mammostrat after primary surgery to inform decisions on the use of adjuvant chemotherapy.

4.2 Three tests (MammaPrint, Oncotype DX and Mammostrat) require that samples are sent to a central laboratory for processing following surgery, with an estimated shipping and processing time of up to 7–10 days. IHC4 is processed in a local laboratory with estimated turnaround times of less than 1 week.

Gene expression profiling

4.3 Some gene expression profiling tests work by identifying and quantifying mRNA transcripts in a specific tissue sample. Because only a fraction of the genes encoded in the genome of a cell are transcribed into mRNA, gene expression profiling provides information about the activity of genes that give rise to these mRNA transcripts. Other gene expression profiling tests work by measuring levels of cDNA, which is synthesised from mRNA. There are a range of different techniques for measuring mRNA levels in breast cancer tumour samples, including real-time reverse transcription polymerase chain reaction (RT‑PCR) and DNA microarrays.

4.4 Different tests use different protocols for preparing the samples (for example, formalin fixation, paraffin embedding, snap freezing and fresh samples) and different methods for preparing the RNA. Furthermore, there are different algorithms for combining the raw data into a summary profile. All of these factors can affect the reproducibility and reliability of gene expression profiling tests.

4.5 The 2 gene expression profiling tests included in this evaluation are described below:

Immunohistochemistry (protein expression profiling)

4.6 Immunohistochemistry tests measure protein levels in the tumour sample rather than RNA or cDNA. Some of these tests offer the advantage of using existing immunohistochemical markers (such as ER and HER2), which are routinely tested in UK pathology departments. The term 'expanded' has been used to describe the immunohistochemistry tests evaluated in this assessment that are used in addition to standard immunohistochemistry testing (such as ER and HER2) for early invasive breast cancer. Immunohistochemistry uses staining to identify protein expression and reports the level of protein expression in tumour tissue. Differences in immunohistochemistry values can be caused by variability in several factors, including fixation of tissue, antigen retrieval (used to enhance staining), reagents, and interpretation.

4.7 The expanded immunohistochemistry tests included in this evaluation are described below:

The comparator

4.8 The comparator is standard practice in England. Although this varies between hospitals, Adjuvant! Online and/or the Nottingham Prognostic Index (NPI) are often used to guide decisions on which patients with early breast cancer should be offered adjuvant chemotherapy. The economic analysis used cancer registry data on levels of chemotherapy prescribing to reflect standard practice in England and, therefore, is likely to incorporate the impact on the decision to use chemotherapy based on a range of different decision tools currently used in the NHS.

4.9 Further information on the importance of individual molecular markers (for example, ER and HER2, which are routinely assessed for early breast cancer) in the decision to offer adjuvant chemotherapy (and other therapies such as endocrine therapy) has led to varying local practice. Although some hospitals use Adjuvant! Online and the NPI in their original forms, others use adaptations of these tools. Adjuvant! Online is often used in conjunction with the HER2 score. Management algorithms based on the combined use of the NPI and molecular markers such as ER and HER2 are also used.