#1: Primary site
#2: Corpus uteri
Source 1: 2016 SEER Manual
Notes: Primary Site
Primary Site/Corpus uteri: Is the primary site C541 (endometrium) or C543 (uterine fundus) when the histology states endometrial adenocarcinoma, endometrioid type, but tumor site states fundus? See Discussion.
Pathology--Final description: Uterus, cervix, bilateral fallopian tubes and ovaries, total hysterectomy and bilateral salpingo-oophorectomy: Endometrial adenocarcinoma, endometrioid type, well differentiated, FIGO 1/3. Myometrial invasion: focal myometrial invasion (30% of myometrium) Tumor size: 2 x2 cm Tumor site: Fundus, exophytic/polypoid lesion Gross description: The 3.0 cm in length by 2.5 cm in diameter triangular endometrium is tan-red and smooth with a 2.0 x 2.0 cm tan-pink, exophytic fundic mass which extends on to both anterior and posterior aspects, 4.1 cm from the os.
We recommend coding endometrium, C541, as the primary site for this case. While coding to fundus would not be incorrect, according to our expert pathologist consultant, "it is more appropriate in a setting in which the region of the uterus is of importance, e.g. with a myoma or a myosarcoma, or if the endometrioid carcinoma were NOT in the endometrium but arising in a focus of adenomyosis within the fundic myometrium…"