It’s no secret that cancer prevention, diagnosis, and treatment have improved over time; in the UK, cancer survival has doubled over the last 40 years (1), while the US has seen the overall cancer death rate decline by 1.4% for women and 1.8% for men per year from 2001 to 2017 (2). An almost unimaginable amount of research has made these changes possible, but today we’ll zoom in on the contributions made with immunohistochemistry (IHC), in which scientists use antibodies that are specific to a particular antigen to investigate its distribution in a tissue of interest (3). Read on to find out more about how scientists are leveraging this powerful methodology to drive cancer research forward, and if you’re interested in more resources on IHC, check out our Immunohistochemistry Resources Page.
Antigens specific to a particular tumor are overexpressed or expressed de novo in many cancers, making IHC an invaluable tool for routine cancer diagnosis. Let’s dig into prostate cancer diagnosis for an example of IHC in action.
Prostate-specific membrane antigen (PSMA) is expressed in more than 90% of prostate cancer cells (4). However, when PSMA was initially characterized, its expression in high-grade prostatic intraepithelial neoplasm (PIN), a precursor to prostate cancer (5), had not been compared with its expression in the full-blown cancer itself. David Bostwick et al. set out to answer this question in a study published in 1998. They performed immunohistochemistry staining for PSMA on 184 tissue samples taken from patients with prostate cancer who had undergone prostatectomies and found that PSMA expression increased from benign cells to high-grade PIN to carcinoma (6). The discovery that PSMA expression is correlated with cancer severity helped to establish it as a key prognostic and diagnostic biomarker.
Our knowledge of PSMA expression has continued to act as a springboard for the development of prostate cancer therapeutics, including a recent breakthrough in imaging to guide treatment decisions. Determining whether a patient’s prostate cancer has metastasized and tracking down distant tumors is challenging, and incorrect diagnosis can result in under- or over-treatment. To solve this problem, researchers developed an injectable PSMA-binding radioactive tracer. After administration, clinicians use position emission tomography (PET) imaging to detect the PSMA-bound tracer and pinpoint tumors throughout the body (7,8). PSMA-PET imaging represents a major advance in prostate cancer diagnostics and identifies cancer that was often missed by previous imaging techniques.
Neuroendocrine tumors affecting the gastrointestinal tract or pancreas (GEP-NETs) are a rare type of cancer that originate from the neuroendocrine cell system (9). These tumors are clinically and biologically heterogenous, but most overexpress somatostatin receptors (SSTRs). For this reason, they are commonly treated with somatostatin analogs or SSTR-targeted radiopharmaceuticals (a type of drug that delivers radiation directly to cancer cells). However, these therapies tend to work best for patients whose tumors overexpress SSTR types 2 and 5 (10).
Hee Sung Kim et al. harnessed IHC to evaluate the clinical significance of the expression of COX-2, another important biomarker in GEP-NETs. By investigating the expression pattern of COX-2 and SSTR types 1, 2, and 5 in 247 GEP-NET samples and correlating these expression patterns with patients’ overall survival, they found that SSTR overexpression was associated with longer overall survival and a favorable prognosis. Conversely, overexpression of COX-2 (found in 54% of GEP-NETs) was associated with a more aggressive cancer and a poor prognosis. Thanks to this discovery, the authors suggested that COX-2 could be a therapeutic target in patients with COX-2-overexpressing GEP-NETs. Indeed, drugs that inhibit COX-2 are already being deployed as adjuvants to chemotherapy in a range of clinical trials to treat metastatic breast cancer, gliomas, and squamous cell carcinoma (11).
When Kimberly Kalli and her colleagues set out to do their ground-breaking work on the folate receptor in ovarian cancer, it was already known to be expressed at levels 10- to 100-fold higher in most ovarian tumors compared with normal tissue (12). To determine whether it was also overexpressed in recurrent and metastatic disease, Kalli and her team carried out IHC on almost 200 primary and recurrent ovarian cancer tissue samples as well as 20 metastatic foci to evaluate folate receptor expression. They discovered that folate receptor expression is elevated in the vast majority of women with ovarian cancer, especially in serious tumors considered high-stage and likely to recur. This means that therapies and diagnostic tools targeting the folate receptor are highly promising for most people suffering from this type of cancer (13).
For proof, look no further than pafolacianine (trade name Cytalux™ from On Target Laboratories), a fluorescent small molecule that improves surgical outcomes for women with ovarian cancer by “highlighting” difficult-to-spot cancerous lesions. In a clinical trial, pafolacianine helped surgeons find and remove additional ovarian cancer lesions in 27% of patients (14). After binding to and being taken up by folate receptor positive cancer cells, pafolacianine is illuminated during surgery and helps guide surgical decision-making. It is especially useful for cancer located below the surface of the tissue, which was easily missed using earlier surgical techniques (15).
The importance of catching cancer early can hardly be overstated: statistics show that for most cancers, the survival rate at one and five years is much higher for those detected at early stages (Stage 1) compared with cancers found at later stages (16). Many cancers can be effectively treated early in disease development, and an ambitious project headed by the National Institute of Cancer aims to take advantage of this fact by making it easier for clinicians to identify and treat pre-cancerous lesions (17). This project, called the Pre Cancer Atlas, aspires to revolutionize cancer prevention by examining the very early molecular and histological changes that take place as cells progress from normal to cancerous (18).
Unsurprisingly, IHC is already playing a starring role. Scientists from the Olivier Harismendy group at UC San Diego investigated the molecular and microenvironmental factors that characterize breast ductal carcinoma in situ (DCIS), an early stage of breast cancer. DCIS is known to be highly heterogeneous, and it is difficult to predict which patients are likely to have recurrent disease (and therefore require aggressive treatment) and which can be safely monitored without additional therapies. Harismendy and his colleagues used multiplex IHC to help paint a more complete picture of the heterogeneity seen in pre-invasive breast cancer by linking histological features of cancerous lesions with changes in immune state and gene expression. This kind of multi-dimensional work is essential to identify the factors that drive malignant progression, both in breast cancer and across other tissues.
Personalized medicine can help predict a person’s risk for developing a particular type of cancer or, if they already have cancer, the likelihood that they will respond well to a specific treatment based on genetic mutations in their cells (germline constitution) or their tumor (somatic mutations) (19,20). IHC plays a central role here, as antibody staining results obtained with IHC are commonly used to identify underlying genetic mutations in tumors (20).
In fact, clinicians are leveraging IHC to provide glioma patients with a personalized prognosis. Mutations in the enzyme isocitrate dehydrogenase 1-coding gene IDH1 are commonly found in gliomas, and help to predict disease outcomes: gliomas with mutations in IDH1 or the closely related IDH2 have an improved prognosis and longer survival times as compared with gliomas with wild-type IDH (21). Clinicians can determine the IDH mutational status of a glioma with mutation-specific IHC, a highly specific and sensitive technique shown to have nearly 100% accuracy in the detection of the IDH1 mutation most frequently seen in this type of cancer (22). Moreover, researchers have high hopes of developing IDH-targeted therapies, meaning that someday soon, healthcare providers could use a glioma patient’s IDH status to help design their personalized treatment plan.
It’s hard to imagine the incredible advances that could be made next in cancer research, but one thing is for sure: Vector Laboratories is here to support scientists in any way that we can. Come back to the blog soon for more stories about cutting-edge research, scientist highlights, and tips and tricks to help you get the most out of your experiments.