Lung cancer patients with diabetes tend to live longer than patients without diabetes, according to a new study from Norway due to be published in the November issue of the Journal of Thoracic Oncology. The researchers did not offer an explanation for the tendency; they suggested it needs further investigation, and diabetes should not be considered as a reason to withhold standard cancer therapy.
In their background information, the researchers, from Norwegian University of Science and Technology and Trondheim University, write that patients with lung cancer often have other diseases, one of them being diabetes. However, evidence on the impact of diabetes on lung cancer survival is conflicting, so they wanted to do a large study focusing on this.
For their analysis they compared survival with and without diabetes in 1,677 lung cancer cases (among which 77 patients had also been diagnosed with diabetes mellitus).
1,031 cases were from the Nord-Trondelag Health Study (HUNT study) linked to the Norwegian Cancer Registry, 436 from the Pemetrexed Gemcitabine (PEG) study, and 210 from the Norwegian Lung Cancer Biobank registry.
The results showed that:
- The 1-year survival rate for patients with lung cancer who also had diabetes was 43% compared to 28% for those without diabetes,
- The 2-year survival rates were 19% and 11% respectively, and
- The 3-year survival rates were 3% and 1% respectively.
- When they adjusted for variables such as gender, age, stage of disease, the hazard ratio for survival in patients with lung cancer and diabetes mellitus was 0.55 (95% CI, 0.41-0.75), indicating that at a point in time, nearly twice as many lung cancer patients without diabetes died compared to those with diabetes.
The researchers concluded that:
“Patients with lung cancer with diabetes mellitus have an increased survival compared with those without diabetes mellitus.”
They also found that patients with diabetes had a lower rate of metastatic cancer, that is they were less likely to have tumors that had spread.
At first they thought this might explain why the patients with diabetes survived longer, because most patients with lung cancer don’t die from the primary tumor but from the secondary tumors.
But, when they investigated further, things were not as straightforward as one might assume. It looks more like diabetes itself may be the important factor:
“… as we adjusted for stage of disease in our analyses this potential advantage can hardly explain the observed increased survival in patients with diabetes mellitus. In addition, increased survival in patients with diabetes mellitus was clearly demonstrated in the PEG study where all patients had advanced lung cancer.”
This is why they called for more research to be done:
“The survival benefit [of diabetes] may be of clinical importance and should be focused on in future studies.”
In the meantime, they recommended:
“Standard therapy should not be withheld from patients with diabetes mellitus provided they are otherwise fit, even if it may be considered a significant comorbidity.”
Written by Catharine Paddock PhD