People with early-stage breast cancer feel less pain when they are given an anesthetic during a test to see if the cancer has spread, according to a study released on Thursday.

Sentinel lymph nodes are often the first place breast cancer goes when it spreads. A radioisotope solution and dye are injected into the area of the tumour and follow the path the cancerous cells are most likely to take, and then the sentinel nodes are biopsied. 

'This study is the first of its kind and the authors should be congratulated for addressing an issue which has been widely ignored by the surgical community.' — Hiram Cody

The approach works, but it is a painful procedure. In Thursday's online issue of Lancet Oncology, U.S. researchers found adding the anesthetic lidocaine reduced injection pain in patients having their sentinel lymph nodes or SLN mapped.

"For centres that use radiocolloid injections for SLN mapping in patients with early breast cancer, the addition of one per cent lidocaine to the radioisotope solution can improve patient comfort, without compromising SLN identification," Dr. Alexander Stojadinovic of the United States Military Cancer Institute in Washington and his colleagues concluded in the study.

The researchers set out to test whether adding the anesthetic or adding sodium bicarbonate to adjust the pH of the isotope solution could help reduce pain.  

The team enrolled 140 participants with early-stage breast cancer. Of these people, equal numbers, 35, were randomly assigned to receive injections of the radioisotope solution alone (standard care), or the radioisotope combined with either sodium bicarbonate, one per cent lidocaine, or sodium bicarbonate plus lidocaine.

Subjects who were injected with radioisotope alone received four per cent topical lidocaine cream, while those in the three other groups used placebo cream.

The 121 participants who completed the mapping were asked to rate their pain at the time of injection and complete a pain-intensity questionnaire. (The other 19 people were excluded from the analysis either because they declined to participate in the trial, received care elsewhere, there were medical or technical issues with mapping, or unreliable data.)

Average scores on the pain rating scale, with zero representing no pain and 10 the most pain, were:

  • Standard care group — 6.0
  • Sodium bicarbonate — 4.7
  • One per cent lidocaine — 1.6
  • Sodium bicarbonate plus one per cent lidocaine — 1.6

Average pain rating intensity, which could range from zero to 78, was 17.5 for the standard care group, 15.4 for the sodium bicarbonate group, 4.6 for the one per cent lidocaine group and 3.4 for the sodium bicarbonate plus one per cent lidocaine group.

The SLN identification rate among those who received the lidocaine mixtures were 90 per cent, which was not significantly different than the 96 per cent and 97 per cent rates in the standard care and bicarbonate-only groups, respectively, the researchers said.

'Many patients will benefit'

Using sodium bicarbonate to make the radioisotope solution less acidic and closer to the physiological pH had little effect on relieving pain, while the lidocaine did.

No adverse events were reported.

"This study is the first of its kind and the authors should be congratulated for addressing an issue which has been widely ignored by the surgical community," Hiram Cody, of the Memorial Sloan-Kettering Cancer Center in New York, wrote in a commentary accompanying the study.

"All of us who use [technetium-sulphur] colloid are well advised to add lidocaine to our injection protocols; many patients will benefit."

Cody also questioned whether all lidocaine solutions used worldwide are equally beneficial, and if changing the volume or site of injection might help.

The study also serves as a reminder that surgery is the most effective therapy for most solid tumours, especially breast cancer, and "sometimes the smallest and simplest of technical modifications can substantially benefit our patients," he concluded.