A novel subclassification of pT2 gastric cancers according to the depth of muscularis propria invasion: superficial muscularis propria versus deep muscularis propria/subserosa.
OBJECTIVE
To propose a novel subclassification of pT2 gastric cancers according to the depth of muscularis propria (MP) invasion (superficial MP vs. deep MP/subserosa [SS]) and to investigate its impact in prognostic assessment.


BACKGROUND
The major change in the sixth edition of the International Union Against Cancer (UICC)/American Joint Committee on Cancer (AJCC) TNM classification concerned the pT (primary tumor) category. Specifically, pT2 lesions were divided into pT2a (invading the MP) and pT2b (invading the SS) to discriminate these intramural locations. However, the value of the modification is still debated.


METHODS
One thousand two hundred fifty-six patients with pT2 cancers classified according to the UICC/AJCC pT staging system were reviewed. Among them, 214 (17.0%) were classified as invasion of the superficial MP (sMP) or inner circular muscle, 163 (13.0%) as invasion of the deep MP (dMP) or outer longitudinal muscle, and 879 (70.0%) as invasion of SS. Clinicopathologic features were compared between patients with sMP, dMP, and SS invasion. Overall survival rates were compared between the pT2a and pT2b stage cancers, according to the UICC/AJCC and the novel pT2 system. Two-step multivariate analysis was performed to identify the significantly important prognostic factors.


RESULTS
There was significant difference in most of the clinicopathologic features between sMP and SS cancers. Although, only 5 factors (tumor location, tumor size, Borrmann type, metastasis number, and metastasis ratio) were significantly different between dMP and SS cancers. In step 1 of the multivariate analysis, the UICC/AJCC pT2 system was an independent factor that correlated with prognosis, but was substituted by the novel pT2 system in step 2 of the multivariate analysis. With a certain metastasis ratio of lymph nodes, the novel pT2 system discriminated 2 subsets of patients with significantly different prognoses, whereas the UICC/AJCC pT2 system did not.


CONCLUSIONS
The novel pT2 staging system, which was subclassified as sMP and dMP/SS cancers, had more potential to identify the different prognoses for patients with pT2 gastric cancers.
Sun
Zhe
Z
Department of Surgical Oncology, First Affiliated Hospital of China Medical University, Shenyang, Liaoning, China.
Zhu
Guo-Lian
GL
Lu
Chong
C
Guo
Peng-Tao
PT
Huang
Bao-Jun
BJ
Li
Kai
K
Xu
Yan
Y
Wang
Zhen-Ning
ZN
Xu
Hui-Mian
HM
D000368:Aged; D005260:Female; D005753:Gastric Mucosa / Q000473:pathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009361:Neoplasm Invasiveness; D009367:Neoplasm Staging; D013274:Stomach Neoplasms / Q000145:classification* / Q000473:pathology*