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VOLUME 7 NUMBER 4 • NOVEMBER 2010
173
You and Your Patient
SA JOURNAL OF DIABETES & VASCULAR DISEASE
YOU AND YOUR PATIENT
Obesity, diabetes and cancer: a complex relationship about which much must still be learned
seem to feed cancers. ‘Reducing glucose lev-
els may therefore reduce the risk’, continues Dr
Liebl.
He feels strongly that all doctors who treat
diabetics needs to be aware of the cancer risk
and send these patients for early screening.
‘Because the risk is indeed partially explained
by obesity, lifestyle changes are very important.
In addition to its other well-documented ben-
efits, weight loss reduces this cancer risk.’ Dr
Liebl underscored too that abdominal obesity is
a more reliable marker of risk than body mass
index (BMI).
In their editorial in Diabetologia,
1
Smith and
Gale drew the following key conclusions:
•
Endogenous insulin increases cancer risk in
obesity and type 2 diabetes.
•
Secretagogues and exogenous insulin may
therefore also affect risk.
•
Risk differences were observed in ‘unprec-
edented’ short time frames.
•
This suggests activation/acceleration of la-
tent foci.
Further to the Diabetologia reports, a consensus
statement by the American Diabetes Association
and American Cancer Society concluded that
there is a risk of certain cancers (liver, pancreas,
colon, breast, endometrium, rectum, bladder)
in diabetes, predominantly in type 2 diabetics.
Possible mechanisms include hyperinsulinae-
mia, hyperglycaemia and inflammation. Healthy
diets, physical activity and weight management
reduce risk and should be actively promoted.
Patients with diabetes should be strongly
encouraged to undergo cancer screening. The
evidence for risk associated with specific treat-
ments is limited and may have been confounded
by other factors; further research is required in
this regard. Cancer risk should not be a major
factor in choosing between available diabetes
S Afr J Diabetes Vasc Dis 2010;
7
: 173.
Interview with Dr Andreas Liebl, Department for Internal Medicine, Centre for Diabetes and Metabolism, Fachklinik Bad Heilbrunn, Germany
report by Peter Wagenaar
treatments for the average patient.
Addressing South African specialists in Jo-
hannesburg recently, Dr Liebl emphasised the
following take-home messages.
•
Type 2 diabetes is a risk factor for cancer,
independent of BMI.
•
Central obesity is probably more strongly
associated with risk for some cancers.
•
Whether the metabolic syndrome per se
is associated with increased cancer risk is
unclear.
•
Polypharmacy confounders include aspirin,
anti-depressants and, possibly, statins.
•
Metformin is likely to be cancer protective
independent of its effects on insulin.
•
Whether sulphonylureas increase cancer
risk is unclear.
•
In vitro mechanisms suggest that the insulin
sensitising TZD may be cancer protective,
but in clinical trials they appear to have a
null effect.
Where insulin is concerned, he feels it’s impor-
tant to avoid unnecessary panic and that doc-
tors not discontinue insulin in their patients. ‘It’s
been shown in diabetic mice with cancer that if
you take away their insulin, tumour growth slows
but they die sooner from acute complications of
their diabetes. We therefore need to modify risk
by careful selection of specific insulins.’
He points out that up to now, the glargine in-
sulin analogue has been suggested to increase
cancer risk whereas other insulin analogues
such as Aspar, Lisp, and Detem have been prov-
en to be safe. However, the findings are equivo-
cal. ‘In my own centre, we use safe alternatives
to glargine in patients with individual cancer
history or a family risk, as well as in diabetic
children’, he concludes.
1. Smith U, Gale EA. Does diabetes therapy influence the
risk of cancer? Diabetologia 2009;
52
(9): 1699–1708.
Diabetes, Insulin and Cancer Risk
Since a series of articles published in Diabe-
tologia in mid-2009 spotlighted a possible link
between diabetes, obesity and certain cancers,
the topic has been discussed extensively within
the worldwide diabetes fraternity. That there
is indeed a connection is now certain, but the
exact nature thereof remains unclear, not least
because there are so many confounding factors
in the mix.
This is the view of Dr Andreas Liebl, Medical
Director, Centre for Diabetes and Metabolism,
Germany. ‘The confusion was exacerbated by
the fact that some studies showed a connec-
tion with specific cancer-promoting factors and
others not. There is also debate about the role
that insulin treatment plays, although it would
appear that insulin is a growth-promoting factor
in existing cancer, rather than a cause thereof.
Insulin glargine, in particular, would appear to
have a “case to answer” in this regard. But that
said, it is not as simple as that.’
‘One also has to look at confounding factors
such as smoking, obesity, age, gender and so-
cial class. Cancer risk increases with age, re-
gardless of other factors. While obesity and type
2 diabetes commonly occur together, the cancer
risk in obese non-diabetics is nonetheless dif-
ferent from that of diabetics. Different cancers
affect the sexes differently; colon cancer for ex-
ample is more elevated in men than in women.
Individuals from higher social classes also seem
to be at lower risk, possibly as a result of better
nutrition.’
A key consideration is that metformin is pro-
tective against cancer, which is not true for insu-
lin and the sulphonylureas. Patients on the lat-
ter two treatments should therefore remain on
metformin, as it reduces their risk in combina-
tion with the other two. Good glycaemic control
is also critical, as high glucose concentrations
