Traditionally, drugs developed for both types of cancer have been largely focused on targeting the hormones involved in the respective diseases. In the field of breast cancer, it seems R&D is progressing faster as a growing number of products are taking a more specific approach, targeting antigens expressed by tumour cells.
According to pharmaceutical database specialists, Pharmaprojects, research efforts into drugs for prostate cancer have focused on acting as luteinising hormone releasing factor agonists (LHRH), which decrease the levels of circulating testosterone known to have a significant effect on prostate cancer.
Further characterization of the pathology of prostate cancer is at an early stage and as prostate-specific membrane antigen antagonists enter clinical development, this is expected to lead to more targeted approaches to treat the diseases.
Ian Lloyd, managing editor for Pharmaprojects told DrugResearcher.com: "R&D has shown a substantial increase over the past few years."
"Breast cancer has an incidence of almost twice that of prostate cancer, so you could make a case for saying the area is underserved, particularly as there is a greater awareness and higher profile for breast cancer from patient activists."
Since 1995, there has been an almost two fold increase in the number of LHRH agonists under development for the treatment of cancer. Since 1997, there has been a progressive increase in the number of LHRH agonists entering Phase II clinical trials.
However the data also shows indicates a decline in the number of LHRH agonists entering preclinical development between 2000-2003.
However, in 2004, the number rose again, suggesting that this was only a temporary decline. This data implies that hormone-dependent therapies remain one of the primary focuses of R&D in prostate cancer therapeutics.
The report goes on to detail the progress made with treatments for breast cancer specifically those that target the hormone oestrogen. Since 1995, there has been a less clear trend in the number of oestrogen antagonists under development for this indication.
The number of drug treatments peaked in 2001 with 21 oestrogen antagonists under development for the treatment of breast cancer. This figure dropped significantly until 2004, where the figure reached 20.
As breast cancer becomes better understood, efforts are progressing and focus is being directed towards targeting tumour-associated antigens rather than hormones.
Over the same period, there was an increase in the number of ErbB-2 tyrosine kinase inhibitors under development for cancer. These products, which target the ErbB-2 tyrosine kinase, also known as Her-2, take a much more targeted approach to tackling breast cancer.
Patients can be tested to see if they have Her-2-expressing breast cancer gene before treatment to see whether an ErbB-2 tyrosine kinase inhibitor will be effective. Such agents include trastuzumab (Herceptin), and may have fewer side-effects compared to hormonal-based drugs. This targeted approach may be the beginning of the 'next-generation' of cancer drugs for this disease.
Lloyd concluded: "I would expect R&D in both cancers to continue to grow in future years and for this growth to outperform drug R&D growth overall."
"Hormonal treatments for such cancers have been a huge success, eg tamoxifen for breast cancer. The point is they are rather blunter instruments compared to targeted therapeutics. Whether the latter will be so successful remains to be seen though."