Since becoming eligible for free breast cancer screening, I've had the dubious pleasure of two mammograms.

I've learned to dread the NHS-headed letter inviting me to attend, because it's one of the most excruciating experiences you can have without actual surgery. The agonising wait for the result is hellish too. Despite this, I've felt privileged to live in a country that offers women such fantastic preventative healthcare. The mantra that early detection is vital was coined in my lifetime, and it's one that women of my generation have gladly embraced.

But increasingly I've come to realise that screening is a double-edged sword. It's easy to wax lyrical about its benefits when results come back clear. When they don't, a woman really does have to dig deep into herself to decide how she will face the future. We all have a choice about whether or not to accept treatment, but if the scan result is unequivocal then there's surely no choice at all, be it surgery, chemo and/or radiotherapy. We're programmed to cling to life no matter what, and according to figures released this week, breast cancer screening saves an estimated 1300 lives each year and reduces the risk of dying from the disease by 20%. Put another way, it prevents the death of one woman in every 235 invited for screening.

But there's a new caveat for our times. The precision of mammogram technology means it can spot things the human hand or eye cannot, and that very early or dormant cancers can be detected along with the more urgent ones. According to the newly published Independent Breast Cancer Screening (IBCS) Review, this has led to the over-diagnosis of three times that number of women, who undergo unnecessary and potentially harmful treatment for cancers they would not otherwise have known about, and which would never have caused a problem in their lifetime. In other words, cancers they would have died with, not of.

What of the patient who is invited for further tests – usually when her mammogram has picked up the tiniest sign, the merest possibility, of something more serious? Ostensibly she has a choice not to proceed with treatment, but is it really possible to ignore such information and hope for the best? The stress of choosing to live with the knowledge that there's something lurking deep inside you, no matter how apparently insignificant, could be as awful as the treatment itself.

The situation is clear-cut for doctors. Because they can't be absolutely sure whether a growth will spread or stay dormant, they err on the side of caution in their quest to save lives – and, perhaps, to avoid potential litigation.

The dislocation between the capability of ever-advancing technology to deliver and our human inadequacy to deal with it won't go away until the machine is invented that can tell us what to excise and what to leave well alone. Yet I wouldn't like to return to the old days. I was surprised to discover recently that breast cancer in women actually peaks at age 85, and there's a sharp decline in surgery after 70, the age at which screening stops. So presumably if an 80-year-old is discovered to have breast cancer it will be because she has found a lump by the old-fashioned means – through manual examination or by checking in the mirror for visible changes such as skin puckering or an unusually inverted nipple. That used to be the only way of detecting breast cancer, and by the time these signs were visible the lump would be more advanced.

One way of re-calibrating the process, as the IBCS Review suggests, would be for the information sent with screening invitation letters to be revised to highlight more clearly the potential risks involved, as well as the benefits. I'd hope that, rather than being discouraged from being scanned, women who read this information and discuss it with loved ones would feel better prepared for the possible consequences and better able to give informed consent. As consumers of such a life-saving service, it's what we need even if it's difficult to accept.

I just hope my courage doesn't desert me the next time I get that letter.