The new 14-storey £160 million cancer centre at Guy's Hospital has now reached its full height.
Breast cancer survivor Diana Crawshaw performed the 'topping out' ceremony on Tuesday by placing a yew tree branch into the roof of the 14-storey building.
She said: "The topping out ceremony celebrates the combined efforts of all those involved in the realisation of a vision.
"Decisions have been made and patients' views listened to as we move towards an integrated cancer service in an outstanding environment."
Dr Majid Kazmi, clinical director of cancer services at Guy's and St Thomas', added: "The new cancer centre at Guy's promises to be a truly world-class facility for cancer patients in south east London and beyond.
"By bringing together treatment and research, we will be able to provide the best and latest treatments for patients."
Architect Ivan Harbour of Rogers Stirk Harbour + Partners added: "We're very proud of the Cancer Centre at Guy's which combines a welcoming and uplifting environment with state-of-the-art treatment facilities.
"Designed on a human scale to provide the best possible experience for patients and their families, it also has the flexibility to adapt to support changing clinical needs over time."
The Guy's cancer centre appeal still has just under £10 million to raise to help provide the finishing touches to the new building – everything from treatment couches and wheelchairs to privacy screens and gym equipment.
Locals are encouraged to donate £5 by texting GUYS to 70800.
Simon Hughes MP said: "The new world class cancer centre at Guy's is on course to be open for the community next year.
"The topping out ceremony celebrated a great partnership between the NHS, Laing O'Rourke and all the other contractors.
"This will be a top quality building giving the most appropriate support and treatment for the thousands of people who have to battle against cancer every year.
"I could not be more proud of this NHS development in Bermondsey, which I have campaigned for and supported for many years."