Elin Jones said the party's three point "Cancer Contract", would help give the NHS the "fundamental change" it needed.
The plans renewed a pledge that patients would get a cancer diagnosis or the all clear within 28 days.
Welsh ministers warned the policy could result in patients being misdiagnosed or waiting longer for treatment.
In October, 81% of patients diagnosed with cancer began treatment within 62 days, well below the 95% target and down from 85.6% in September.
In December, Deputy Health Minister Vaughan Gething announced 100-day plans had been drawn up by health boards to improve cancer services and waiting times.
On Tuesday, Ms Jones said Labour ministers had not met their own performance targets for the NHS over the past five years.
"We think there needs to be fundamental change there, and that's why we're putting forward interesting and radical proposals for the future of the NHS," she told BBC Wales.
Plaid also promised a "new treatments fund" would improve access to new cancer drugs "based on what your doctor prescribe not your postcode", as well as one-to-one support for all patients before, during and after cancer treatment.
A Welsh government spokesman said: "The majority of people diagnosed with cancer are diagnosed within the first half of the 62-day pathway but the length of time to diagnosis can vary for clinical reasons - lung cancers can be very difficult to diagnose, for example.
"We would reject any idea that would potentially lead to patients being misdiagnosed, not being diagnosed at all to meet a new target or any proposal that would lengthen the time patients wait to start treatment."
The Welsh Conservatives accused Plaid Cymru of producing a "pale imitation" of their Cancer Patients Fund.
The future of the Welsh NHS will be Plaid Cymru's "top priority" in May's assembly election, its health spokeswoman has said.