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Patient had an appendectomy revealing a low grade mucinous appendiceal neoplasm (LAMN) with diffuse peritoneal dissemination. Patient now with cytoreduction and hyperthermic intraperitoneal chemotherapy (HIPEC), which revealed metastatic disease in the abdomen, omentum, pelvic peritoneum, peri-cecal, and gallbladder.

Endocrine mucin-producing sweat gland carcinoma (EMPSCG) is a rare type of low-grade sweat gland carcinoma. Some journal articles indicate that most patients with EMPSCG have coexisting mucinous carcinomas, suggesting that EMPSCG is a precursor to invasive mucinous carcinoma of the skin. Sweat gland carcinoma has its own histology code per the ICD-O-3 (8400/3); should an endocrine mucin-producing sweat gland carcinoma also be coded as 8400/3? If so, would the correct histology for the skin case above be mucinous carcinoma (8480/3) per Rule H17? Conversely, if the terms "mucin-producing" are referring to mucin-producing carcinoma, and not referring to the sweat gland carcinoma, would the histology be coded 8481/3 (mucin-producing carcinoma)?

Pathologists rarely diagnose a GIST as a malignant tumor. Per the AJCC, GISTs encompass a continuum in terms of biologic potential, with larger more mitotically active tumors landing on the "histologically sarcomatous" or malignant end of the spectrum. Because the pathologists generally do not categorize these tumors as benign or malignant, the judgement is typically made by the clinician in light of all the clinical and pathologic findings. Unless there are obvious distant metastases, the clinician usually decides whether a GIST is malignant and treats the patient as such.

In the case above, the patient underwent a gastric biopsy on 04/10/2014 that showed GIST. The subsequent resection on 04/12/2014 showed a 4.5 cm GIST, spindle cell type with 6 mitoses/5 square mm. The resection pathology report does not indicate the GIST is malignant, but does identify a large tumor with mitotic activity. After reviewing the evidence in this case, the clinician calls this a malignant GIST on 04/29/2014 and starts the patient on Gleevec.

Although neither the biopsy nor the resection call this a malignant tumor, should the date the GIST was first diagnosed (biopsy on 04/10/2014) be used to code the diagnosis date, since this is the date the tumor (ultimately felt to be malignant) was diagnosed? If the diagnosis date is coded as the date malignant GIST was first mentioned (04/29/2014), this would exclude surgery as treatment for this tumor.

Would this be a histologic diagnosis because the tumor was histologically confirmed to be GIST? Or must this be a clinical diagnosis because the diagnosis of malignancy was only made clinically (by the clinician's review of the clinical and pathologic findings)?

The MP/H Equivalent Terms and Definitions for Colon indicate that type, subtype, predominantly, with features of, major, or with ___ differentiation are all equivalent in terms of coding histology. However, this is not indicated in the General Instructions (e.g., Histologic Type ICD-O-3 or General Instructions Histology Coding Rules). It also is not included as a Note under the Rules where one would expect to use these terms, for example, Rule H7. Is this an oversight or error in the Manual?

In this case, Rule H7 seems to be the first (and most appropriate) rule that applies to this mixed histology tumor. However, the specific histology terms that an invasive tumor may be identified as, are only listed under Rule H13. Can these same terms be used when applying rules for which they are not specifically noted? It would seem logical to use the equivalent histology terms to code a mixed histology tumor identified as a subtype or with features, etc., despite the fact that the specific terms are not listed under Rule H7.

4/10/13 Partial hepatectomy: well differentiated mucin producing adenoca involve right and left hepatic ducts, common hepatic duct & common bile duct. Invasion beyond wall of bile duct. CT Scan after 1st surgery shows residual neoplasm cannot be excluded

7/31/13 Left lateral segmentectomy: residual well differentiated cholangiiocarcinoma involving connective tissue surrounding major bile ducts. Per medical director, histolgically code to cholangiocarcinoma.

Primary site: Extra hepatic bile duct. Chemo (5FU, Leucovorin, Oxaliplatin) was started 5/1.

Breast biopsy (from hospital A): DCIS, solid, cribriform, comedo type, high nuclear grade

Breast Lumpectomy (from hospital B): DCIS, cribriform type, nuclear grade 1, tumor 2.5cm