Given an abstract, generate a keyword (a noun phrase) that best describes the focus or contribution of the paper. Such keywords can be directly from the given abstract or outside it.

Let me give you an example: Abstract: Some patients converted from ventricular fibrillation to organized rhythms by defibrillation - trained ambulance technicians(EMT - Ds) will refibrillate before hospital arrival.The authors analyzed 271 cases of ventricular fibrillation managed by EMT - Ds working without paramedic back - up.Of 111 patients initially converted to organized rhythms, 19(17 % ) refibrillated, 11(58 % ) of whom were reconverted to perfusing rhythms, including nine of 11(82 % ) who had spontaneous pulses prior to refibrillation.Among patients initially converted to organized rhythms, hospital admission rates were lower for patients who refibrillated than for patients who did not(53 % versus 76 % , P = NS), although discharge rates were virtually identical(37 % and 35 % , respectively).Scene - to - hospital transport times were not predictively associated with either the frequency of refibrillation or patient outcome.Defibrillation - trained EMTs can effectively manage refibrillation with additional shocks and are not at a significant disadvantage when paramedic back - up is not available.
The answer to this example can be: Ventricular Fibrillation
Here is why: This term is directly present in the abstract and it is one of the main topic in it. So can be chosen as the medical subject heading.

OK. solve this:
Abstract: Seventy-seven samples of healthy and diseased vulvar epithelium (one per patient) were processed using the carbon-coated-dextran biochemical technique. The results were analyzed according to Scatchard or the unique point technique. The samples of normal tissue were obtained from patients who underwent surgical procedures for different gynecologic pathologies. The samples of diseased tissue were obtained with punch biopsy from patients with several vulvar disorders. Ten samples were obtained from the episiotomy wound in pregnant patients during labor. Estrogen receptors were assayed in all cases. Progesterone receptors were assayed simultaneously in 73 of the cases. The minimum concentration considered positive was 2 fmol/mg of protein. A map of the vulvar region was drawn, and samples were obtained from different sites whenever possible.
Answer:
Comparative Study