Intended for healthcare professionals

CCBYNC Open access

Rapid response to:

Research

Effect of mammography screening on surgical treatment for breast cancer in Norway: comparative analysis of cancer registry data

BMJ 2011; 343 doi: https://doi.org/10.1136/bmj.d4692 (Published 13 September 2011) Cite this as: BMJ 2011;343:d4692

Rapid Response:

Authors' reply

We appreciate the response from Hayes et al. Their data suggest an
initial rise in the number of mastectomies caused by high detection rates
of invasive cancer and DCIS during the first screening rounds in the Irish
screening program. Later the mastectomy rates levelled off at about 90 per
100 000 invited. These results are very similar to those in the
corresponding age group in Norway. However, the letter from Hayes et al.
does not include the trends in mastectomy rates in the non-invited women
below age 50 years, so we cannot compare with period trends.

The arguments of Paci et al. rely on two central dogmas of screening.
One is that most invasive breast cancers grow monotonously from a small
size tumour detectable by screening to a large size tumour causing
symptoms. The other is that a high incidence of stage I cancers among
invited women reflects early diagnosis and therefore predicts a
proportional decline in the numbers of advanced cancers when the lead time
has passed.

Both dogmas are wrong. 15 years after screening introduction, there
is no evidence for a compensatory incidence decline for advanced cancers
in Norway. We have shown that overdiagnosis (and not lead time) explains
the screening associated incidence increase in Norway (1) and in other
countries (2). Moreover, more detailed analyses of the incidence data show
that the normal fate of overdiagnosed cancers is to exhibit non-monotonous
growth and undergo spontaneous regression (3,4). For overdiagnosed lesions
the notion "lead time" has no meaning since these neoplasms will never
cause symptoms. Lead-time models for breast cancer growth are widely used
to predict future effects of mammography screening (5). Such models are
worthless and utterly confusing since they are clearly based on erroneous
assumptions.

Mokbel suggests that the high mastectomy rate during the early years
of the Norwegian screening program may reflect the inexperience of the
teams in dealing with impalpable breast cancers in Norway. However, the
introduction of screening in Norway was well organized from the start. The
women were diagnosed and treated at breast diagnostic centres. Surgery was
performed by skilled teams that followed the same guidelines. Patients
with impalpable tumours were offered breast conserving treatment and the
lesions were localized and marked prior to surgery.

1. Zahl PH, Strand BH, Maehlen J. Incidence of breast cancer in
Norway and Sweden during introduction of nationwide screening: prospective
cohort study. BMJ 2004; 328:921-924.

2. Jorgensen KJ, Gotzsche PC. Overdiagnosis in publicly organised
mammography screening programmes: systematic review of incidence trends.
BMJ 2009; 339:b2587.

3. Zahl PH, Maehlen J, Welch HG. The natural history of invasive breast
cancers detected by screening mammography. Arch Intern Med 2008; 168:2311-2316.

4. Zahl PH, Gotzsche PC, Maehlen J. Natural history of breast cancers
detected in the Swedish mammography screening programme: a cohort study.
Lancet Oncol 2011. DOI: 10.1016/S1470-2045(11)70250-9

5. Duffy SW, Lynge E, Jonsson H, Ayyaz S, Olsen AH. Complexities in the
estimation of overdiagnosis in breast cancer screening. Br J Cancer 2008;
99: 1176-1178

Competing interests: No competing interests

01 November 2011
Pal Suhrke
PhD candidate
Jan Maehlen, Ellen Schlichting, Karsten Juhl Jorgensen, Peter C Gotzsche, and Per-Henrik Zahl
Oslo University Hospital