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.
One 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.
Solution is here: Ventricular Fibrillation
Explanation: 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.

Now, solve this: Abstract: With the advent of systemic chemotherapy capable of controlling metastases at most sites, central nervous system metastases are becoming more common in patients with epithelial ovarian carcinoma. A retrospective epidemiologic review at The University of Texas M. D. Anderson Hospital and Tumor Institute revealed central nervous system metastases in 13 of 4456 patients with epithelial ovarian carcinoma (0.29%) registered between 1944 and 1984. No patients were identified as having central nervous system metastases before 1968. The median survival overall was 29 months; following the diagnosis of brain metastases it was five months. Five of eight patients treated for central nervous system metastases lived ten months or longer. Patients with isolated metastases to the central nervous system lived longer than patients with accompanying systemic metastases. Patients treated with surgical resection lived longer than those who did not undergo surgery. With surgical resection, postoperative irradiation, and systemic chemotherapy, significant symptomatic improvement and long-term remission are possible.
Solution:
Adenocarcinoma