when did patient 17398 receive the last microbiology test of the biopsy since 180 months ago?
select microbiologyevents.charttime from microbiologyevents where microbiologyevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 17398 ) and microbiologyevents.spec_type_desc = 'biopsy' and datetime(microbiologyevents.charttime) >= datetime(current_time,'-180 month') order by microbiologyevents.charttime desc limit 1