Cancer and Total Hip Replacement. Cancer as a risk factor for prosthesis and prosthesis as a risk factor for cancer
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Annually, 14 million new cancer cases are detected worldwide; the numbers are expected to rise by 70% over the next decades. In Norway, 30,000 new cancer cases are detected every year. Because of screenings and increased attention to cancer in the population, more cancer cases are detected at an early stage and a higher number of cancer diagnoses are detected. Results of better and earlier treatment are that patients survive and continue to live for many years after a cancer diagnosis.
In Western countries, total hip replacements have become a common treatment for hip joint disease and injury. Standards of living have risen and people are living longer, hence Western populations have an increased proportion of elderly people. Better anaesthetics, lower risks associated with surgery and better quality of prostheses enable both younger and older patients with good general health to receive total hip replacements. In Norway almost 8,000 primary total hip replacement operations are performed annually.
All papers in this thesis are based on a linkage between the Cancer Registry of Norway and the Norwegian Arthroplasty Register.
In this thesis there are two different aspects. The first aspect is the cancer patients; if they survive cancer and live on for many years, there is a risk for developing other diseases and disorders. These may be late effects related to the treatment they received for cancer. In this thesis we consider damage to bone and cartilage in the hip. Our outcome measurement is the insertion of a total hip replacement.
The second aspect is the patients who have received a total hip replacement. Could insertion of metal prosthesis with or without bone cement in the hip joint increase the patient's risk for late development of cancer?
In Paper 1 we selected cancer patients who were 16-90 years old when their first cancer was diagnosed, had no hip replacement prior to the cancer diagnosis and were alive when the Norwegian Arthroplasty Register started registration (September 1987). We compared the observed hip replacement patients with incidence in the general population. Cancer patients were divided in groups according to the location of the cancer and compared. We found an increased risk for hip replacement for patients with lymphoma malignancies and cancer in the pelvic area.
In Paper 2 we selected two groups of cancer patients to investigate whether radiation to the pelvic area increased the risk for total hip replacement. We included women only; one group consisted of patients with gynaecological cancer and radiation to the pelvic area while the other group consisted of breast cancer patients with radiation to the breast and not to the pelvic area. The mortality differed greatly in the two groups, so we used competing risk models to estimate the risk for receiving prosthesis. We found no statistically increased risk for hip replacements for patients with gynaecological cancer compared to patients with breast cancer.
In Paper 3 we selected patients with total hip replacement. We compared their cancer risk to the general population in Norway. We also used Cox models and competing risk models with time-dependent covariates to compare different prosthesis fixations. We found an increased risk of cancer for patients with uncemented total hip replacement compared to patients with cemented total hip replacement. Patients with a combination of cemented cup and uncemented stem (reversed hybrid) had a similar risk for cancer as those with uncemented prosthesis.
The overall conclusion in this thesis is that we found a relation between cancer and total hip replacements. There seems to be an increased risk for hip replacements for some cancer types, but we could not find any increased risk due to irradiation of the hips. For patients who have had a hip replacement for more than 10 years, uncemented prosthesis seems to increase the risk of cancer.