l = ['carcinoma brca positive completion mastectomy',
     'clinical brca gene mutation',
     'carcinoma brca positive chemotherapy']
df = pd.DataFrame(l, columns=['Text'])
df['Gene'] = df['Text'].str.extract(r"(brca)")

Text    Gene
0   breast invasive lobular carcinoma brca positiv...   brca
1   clinical history brca gene mutation . gross de...   brca
2   left breast invasive ductal carcinoma brca pos...   brca

Text    Gene  NextWord
0   breast invasive lobular carcinoma brca positiv...   brca  positive
1   clinical history brca gene mutation . gross de...   brca  gene
2   left breast invasive ductal carcinoma brca pos...   brca  positive