New insights into the treatment of colorectal cancer in the elderly

Two of her studies involve over 4,000 patients (aged 70 and older) who underwent surgery for stage III colorectal cancer between 2011 and 2021.

The aim was to investigate whether there is variation in the use of chemotherapy for these patients, and how the timing of the initiation of chemotherapy after surgery affects survival five years post-treatment.

Significant differences in treatment

The first study examined who received chemotherapy after surgery (adjuvant chemotherapy), based on factors including socioeconomic status (income and education) and place of residence, as well as the timing of initiation. According to Norwegian guidelines, treatment should commence within six weeks after surgery.

The findings show that only 13 per cent of patients received chemotherapy within six weeks, and 26 per cent within eight weeks. In practice, this means that it is equally common for older patients to start chemotherapy in week seven or eight as within the first six weeks after surgery. Furthermore, one in five patients started later than eight weeks. There was also a significant proportion of patients who never received chemotherapy.

The patients' socioeconomic status had a considerable impact:

— Patients with low socioeconomic status had significantly less chance of starting treatment both within six and eight weeks compared to patients with high socioeconomic status. Additionally, older individuals living alone had less chance of receiving treatment than those living with a partner, explains postdoctoral researcher at SKDE, Elin Marthinussen Gustavsen.

Geographical variation

Moreover, the study revealed geographical differences in who received chemotherapy. The geographical variation was also different for initiation within six and eight weeks. In some geographical areas, patients had a higher chance of starting treatment within eight weeks than within six weeks, and vice versa. Other areas had consistently low or high levels depending on the timing.

According to Gustavsen, this may indicate differing practices and interpretations of the guidelines between catchment areas.

Chemotherapy can start later

The second study investigated how the timing of the initiation of chemotherapy affects survival. Gustavsen found that starting chemotherapy within eight weeks after surgery provides the best possible survival for older patients with stage III colorectal cancer. For certain patients—particularly those with a higher risk profile—treatment may still be beneficial when it starts up to 10 weeks after surgery. Only when treatment was delayed more than 10 weeks did survival clearly decline.

— Our findings suggest that there is room for greater flexibility in the initiation of chemotherapy for older patients compared to current recommendations. Many older individuals need more time to recover after surgery, and a more flexible timeframe would make it easier to tailor treatment to the individual, says Elin Marthinussen Gustavsen.

Doctoral research on older patients and cancer

On 25 April 2025, Elin Marthinussen Gustavsen defended her PhD thesis at UiT The Arctic University of Norway entitled Variation in cancer treatment of elderly patients in Norway - Geographic, socioeconomic, and impact of timing.

In addition to the two studies on colorectal cancer, the doctoral research includes a study on differences in the treatment of older patients (aged 70 or older) with high-risk prostate cancer.